why is a literature review important to a research study

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The Literature Review: A Foundation for High-Quality Medical Education Research

a  These are subscription resources. Researchers should check with their librarian to determine their access rights.

Despite a surge in published scholarship in medical education 1 and rapid growth in journals that publish educational research, manuscript acceptance rates continue to fall. 2 Failure to conduct a thorough, accurate, and up-to-date literature review identifying an important problem and placing the study in context is consistently identified as one of the top reasons for rejection. 3 , 4 The purpose of this editorial is to provide a road map and practical recommendations for planning a literature review. By understanding the goals of a literature review and following a few basic processes, authors can enhance both the quality of their educational research and the likelihood of publication in the Journal of Graduate Medical Education ( JGME ) and in other journals.

The Literature Review Defined

In medical education, no organization has articulated a formal definition of a literature review for a research paper; thus, a literature review can take a number of forms. Depending on the type of article, target journal, and specific topic, these forms will vary in methodology, rigor, and depth. Several organizations have published guidelines for conducting an intensive literature search intended for formal systematic reviews, both broadly (eg, PRISMA) 5 and within medical education, 6 and there are excellent commentaries to guide authors of systematic reviews. 7 , 8

• A literature review forms the basis for high-quality medical education research and helps maximize relevance, originality, generalizability, and impact.
• A literature review provides context, informs methodology, maximizes innovation, avoids duplicative research, and ensures that professional standards are met.
• Literature reviews take time, are iterative, and should continue throughout the research process.
• Researchers should maximize the use of human resources (librarians, colleagues), search tools (databases/search engines), and existing literature (related articles).
• Keeping organized is critical.

Such work is outside the scope of this article, which focuses on literature reviews to inform reports of original medical education research. We define such a literature review as a synthetic review and summary of what is known and unknown regarding the topic of a scholarly body of work, including the current work's place within the existing knowledge . While this type of literature review may not require the intensive search processes mandated by systematic reviews, it merits a thoughtful and rigorous approach.

Purpose and Importance of the Literature Review

An understanding of the current literature is critical for all phases of a research study. Lingard 9 recently invoked the “journal-as-conversation” metaphor as a way of understanding how one's research fits into the larger medical education conversation. As she described it: “Imagine yourself joining a conversation at a social event. After you hang about eavesdropping to get the drift of what's being said (the conversational equivalent of the literature review), you join the conversation with a contribution that signals your shared interest in the topic, your knowledge of what's already been said, and your intention.” 9

The literature review helps any researcher “join the conversation” by providing context, informing methodology, identifying innovation, minimizing duplicative research, and ensuring that professional standards are met. Understanding the current literature also promotes scholarship, as proposed by Boyer, 10 by contributing to 5 of the 6 standards by which scholarly work should be evaluated. 11 Specifically, the review helps the researcher (1) articulate clear goals, (2) show evidence of adequate preparation, (3) select appropriate methods, (4) communicate relevant results, and (5) engage in reflective critique.

Failure to conduct a high-quality literature review is associated with several problems identified in the medical education literature, including studies that are repetitive, not grounded in theory, methodologically weak, and fail to expand knowledge beyond a single setting. 12 Indeed, medical education scholars complain that many studies repeat work already published and contribute little new knowledge—a likely cause of which is failure to conduct a proper literature review. 3 , 4

Likewise, studies that lack theoretical grounding or a conceptual framework make study design and interpretation difficult. 13 When theory is used in medical education studies, it is often invoked at a superficial level. As Norman 14 noted, when theory is used appropriately, it helps articulate variables that might be linked together and why, and it allows the researcher to make hypotheses and define a study's context and scope. Ultimately, a proper literature review is a first critical step toward identifying relevant conceptual frameworks.

Another problem is that many medical education studies are methodologically weak. 12 Good research requires trained investigators who can articulate relevant research questions, operationally define variables of interest, and choose the best method for specific research questions. Conducting a proper literature review helps both novice and experienced researchers select rigorous research methodologies.

Finally, many studies in medical education are “one-offs,” that is, single studies undertaken because the opportunity presented itself locally. Such studies frequently are not oriented toward progressive knowledge building and generalization to other settings. A firm grasp of the literature can encourage a programmatic approach to research.

Approaching the Literature Review

Considering these issues, journals have a responsibility to demand from authors a thoughtful synthesis of their study's position within the field, and it is the authors' responsibility to provide such a synthesis, based on a literature review. The aforementioned purposes of the literature review mandate that the review occurs throughout all phases of a study, from conception and design, to implementation and analysis, to manuscript preparation and submission.

Planning the literature review requires understanding of journal requirements, which vary greatly by journal ( table 1 ). Authors are advised to take note of common problems with reporting results of the literature review. Table 2 lists the most common problems that we have encountered as authors, reviewers, and editors.

Sample of Journals' Author Instructions for Literature Reviews Conducted as Part of Original Research Article a

Common Problem Areas for Reporting Literature Reviews in the Context of Scholarly Articles

Locating and Organizing the Literature

Three resources may facilitate identifying relevant literature: human resources, search tools, and related literature. As the process requires time, it is important to begin searching for literature early in the process (ie, the study design phase). Identifying and understanding relevant studies will increase the likelihood of designing a relevant, adaptable, generalizable, and novel study that is based on educational or learning theory and can maximize impact.

Human Resources

A medical librarian can help translate research interests into an effective search strategy, familiarize researchers with available information resources, provide information on organizing information, and introduce strategies for keeping current with emerging research. Often, librarians are also aware of research across their institutions and may be able to connect researchers with similar interests. Reaching out to colleagues for suggestions may help researchers quickly locate resources that would not otherwise be on their radar.

During this process, researchers will likely identify other researchers writing on aspects of their topic. Researchers should consider searching for the publications of these relevant researchers (see table 3 for search strategies). Additionally, institutional websites may include curriculum vitae of such relevant faculty with access to their entire publication record, including difficult to locate publications, such as book chapters, dissertations, and technical reports.

Strategies for Finding Related Researcher Publications in Databases and Search Engines

Search Tools and Related Literature

Researchers will locate the majority of needed information using databases and search engines. Excellent resources are available to guide researchers in the mechanics of literature searches. 15 , 16

Because medical education research draws on a variety of disciplines, researchers should include search tools with coverage beyond medicine (eg, psychology, nursing, education, and anthropology) and that cover several publication types, such as reports, standards, conference abstracts, and book chapters (see the box for several information resources). Many search tools include options for viewing citations of selected articles. Examining cited references provides additional articles for review and a sense of the influence of the selected article on its field.

Box Information Resources

• Web of Science a
• Education Resource Information Center (ERIC)
• Cumulative Index of Nursing & Allied Health (CINAHL) a
• Google Scholar

Once relevant articles are located, it is useful to mine those articles for additional citations. One strategy is to examine references of key articles, especially review articles, for relevant citations.

Getting Organized

As the aforementioned resources will likely provide a tremendous amount of information, organization is crucial. Researchers should determine which details are most important to their study (eg, participants, setting, methods, and outcomes) and generate a strategy for keeping those details organized and accessible. Increasingly, researchers utilize digital tools, such as Evernote, to capture such information, which enables accessibility across digital workspaces and search capabilities. Use of citation managers can also be helpful as they store citations and, in some cases, can generate bibliographies ( table 4 ).

Citation Managers

Knowing When to Say When

Researchers often ask how to know when they have located enough citations. Unfortunately, there is no magic or ideal number of citations to collect. One strategy for checking coverage of the literature is to inspect references of relevant articles. As researchers review references they will start noticing a repetition of the same articles with few new articles appearing. This can indicate that the researcher has covered the literature base on a particular topic.

Putting It All Together

In preparing to write a research paper, it is important to consider which citations to include and how they will inform the introduction and discussion sections. The “Instructions to Authors” for the targeted journal will often provide guidance on structuring the literature review (or introduction) and the number of total citations permitted for each article category. Reviewing articles of similar type published in the targeted journal can also provide guidance regarding structure and average lengths of the introduction and discussion sections.

When selecting references for the introduction consider those that illustrate core background theoretical and methodological concepts, as well as recent relevant studies. The introduction should be brief and present references not as a laundry list or narrative of available literature, but rather as a synthesized summary to provide context for the current study and to identify the gap in the literature that the study intends to fill. For the discussion, citations should be thoughtfully selected to compare and contrast the present study's findings with the current literature and to indicate how the present study moves the field forward.

To facilitate writing a literature review, journals are increasingly providing helpful features to guide authors. For example, the resources available through JGME include several articles on writing. 17 The journal Perspectives on Medical Education recently launched “The Writer's Craft,” which is intended to help medical educators improve their writing. Additionally, many institutions have writing centers that provide web-based materials on writing a literature review, and some even have writing coaches.

The literature review is a vital part of medical education research and should occur throughout the research process to help researchers design a strong study and effectively communicate study results and importance. To achieve these goals, researchers are advised to plan and execute the literature review carefully. The guidance in this editorial provides considerations and recommendations that may improve the quality of literature reviews.

Why is it important to do a literature review in research?

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 “A substantive, thorough, sophisticated literature review is a precondition for doing substantive, thorough, sophisticated research”. Boote and Baile 2005

Authors of manuscripts treat writing a literature review as a routine work or a mere formality. But a seasoned one knows the purpose and importance of a well-written literature review.  Since it is one of the basic needs for researches at any level, they have to be done vigilantly. Only then the reader will know that the basics of research have not been neglected.

The aim of any literature review is to summarize and synthesize the arguments and ideas of existing knowledge in a particular field without adding any new contributions.   Being built on existing knowledge they help the researcher to even turn the wheels of the topic of research.  It is possible only with profound knowledge of what is wrong in the existing findings in detail to overpower them.  For other researches, the literature review gives the direction to be headed for its success. 

The common perception of literature review and reality:

As per the common belief, literature reviews are only a summary of the sources related to the research. And many authors of scientific manuscripts believe that they are only surveys of what are the researches are done on the chosen topic.  But on the contrary, it uses published information from pertinent and relevant sources like

• Scholarly books
• Scientific papers
• Latest studies in the field
• Established school of thoughts
• Relevant articles from renowned scientific journals

and many more for a field of study or theory or a particular problem to do the following:

• Summarize into a brief account of all information
• Synthesize the information by restructuring and reorganizing
• Critical evaluation of a concept or a school of thought or ideas
• Familiarize the authors to the extent of knowledge in the particular field
• Encapsulate
• Compare & contrast

By doing the above on the relevant information, it provides the reader of the scientific manuscript with the following for a better understanding of it:

• It establishes the authors’  in-depth understanding and knowledge of their field subject
• It gives the background of the research
• Portrays the scientific manuscript plan of examining the research result
• Illuminates on how the knowledge has changed within the field
• Highlights what has already been done in a particular field
• Information of the generally accepted facts, emerging and current state of the topic of research
• Identifies the research gap that is still unexplored or under-researched fields
• Demonstrates how the research fits within a larger field of study
• Provides an overview of the sources explored during the research of a particular topic

Importance of literature review in research:

The importance of literature review in scientific manuscripts can be condensed into an analytical feature to enable the multifold reach of its significance.  It adds value to the legitimacy of the research in many ways:

• Provides the interpretation of existing literature in light of updated developments in the field to help in establishing the consistency in knowledge and relevancy of existing materials
• It helps in calculating the impact of the latest information in the field by mapping their progress of knowledge.
• It brings out the dialects of contradictions between various thoughts within the field to establish facts
• The research gaps scrutinized initially are further explored to establish the latest facts of theories to add value to the field
• Indicates the current research place in the schema of a particular field
• Provides information for relevancy and coherency to check the research
• Apart from elucidating the continuance of knowledge, it also points out areas that require further investigation and thus aid as a starting point of any future research
• Justifies the research and sets up the research question
• Sets up a theoretical framework comprising the concepts and theories of the research upon which its success can be judged
• Helps to adopt a more appropriate methodology for the research by examining the strengths and weaknesses of existing research in the same field
• Increases the significance of the results by comparing it with the existing literature
• Provides a point of reference by writing the findings in the scientific manuscript
• Helps to get the due credit from the audience for having done the fact-finding and fact-checking mission in the scientific manuscripts
• The more the reference of relevant sources of it could increase more of its trustworthiness with the readers
• Helps to prevent plagiarism by tailoring and uniquely tweaking the scientific manuscript not to repeat other’s original idea
• By preventing plagiarism , it saves the scientific manuscript from rejection and thus also saves a lot of time and money
• Helps to evaluate, condense and synthesize gist in the author’s own words to sharpen the research focus
• Helps to compare and contrast to  show the originality and uniqueness of the research than that of the existing other researches
• Rationalizes the need for conducting the particular research in a specified field
• Helps to collect data accurately for allowing any new methodology of research than the existing ones
• Enables the readers of the manuscript to answer the following questions of its readers for its better chances for publication
• What do the researchers know?
• What do they not know?
• Is the scientific manuscript reliable and trustworthy?
• What are the knowledge gaps of the researcher?

22. It helps the readers to identify the following for further reading of the scientific manuscript:

• What has been already established, discredited and accepted in the particular field of research
• Areas of controversy and conflicts among different schools of thought
• Unsolved problems and issues in the connected field of research
• The emerging trends and approaches
• How the research extends, builds upon and leaves behind from the previous research

A profound literature review with many relevant sources of reference will enhance the chances of the scientific manuscript publication in renowned and reputed scientific journals .

References:

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• Research Process

Literature Review in Research Writing

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Table of Contents

Research on research? If you find this idea rather peculiar, know that nowadays, with the huge amount of information produced daily all around the world, it is becoming more and more difficult to keep up to date with all of it. In addition to the sheer amount of research, there is also its origin. We are witnessing the economic and intellectual emergence of countries like China, Brazil, Turkey, and United Arab Emirates, for example, that are producing scholarly literature in their own languages. So, apart from the effort of gathering information, there must also be translators prepared to unify all of it in a single language to be the object of the literature survey. At Elsevier, our team of translators is ready to support researchers by delivering high-quality scientific translations , in several languages, to serve their research – no matter the topic.

What is a literature review?

A literature review is a study – or, more accurately, a survey – involving scholarly material, with the aim to discuss published information about a specific topic or research question. Therefore, to write a literature review, it is compulsory that you are a real expert in the object of study. The results and findings will be published and made available to the public, namely scientists working in the same area of research.

How to Write a Literature Review

First of all, don’t forget that writing a literature review is a great responsibility. It’s a document that is expected to be highly reliable, especially concerning its sources and findings. You have to feel intellectually comfortable in the area of study and highly proficient in the target language; misconceptions and errors do not have a place in a document as important as a literature review. In fact, you might want to consider text editing services, like those offered at Elsevier, to make sure your literature is following the highest standards of text quality. You want to make sure your literature review is memorable by its novelty and quality rather than language errors.

Writing a literature review requires expertise but also organization. We cannot teach you about your topic of research, but we can provide a few steps to guide you through conducting a literature review:

• Choose your topic or research question: It should not be too comprehensive or too limited. You have to complete your task within a feasible time frame.
• Set the scope: Define boundaries concerning the number of sources, time frame to be covered, geographical area, etc.
• Decide which databases you will use for your searches: In order to search the best viable sources for your literature review, use highly regarded, comprehensive databases to get a big picture of the literature related to your topic.
• Search, search, and search: Now you’ll start to investigate the research on your topic. It’s critical that you keep track of all the sources. Start by looking at research abstracts in detail to see if their respective studies relate to or are useful for your own work. Next, search for bibliographies and references that can help you broaden your list of resources. Choose the most relevant literature and remember to keep notes of their bibliographic references to be used later on.
• Review all the literature, appraising carefully it’s content: After reading the study’s abstract, pay attention to the rest of the content of the articles you deem the “most relevant.” Identify methodologies, the most important questions they address, if they are well-designed and executed, and if they are cited enough, etc.

If it’s the first time you’ve published a literature review, note that it is important to follow a special structure. Just like in a thesis, for example, it is expected that you have an introduction – giving the general idea of the central topic and organizational pattern – a body – which contains the actual discussion of the sources – and finally the conclusion or recommendations – where you bring forward whatever you have drawn from the reviewed literature. The conclusion may even suggest there are no agreeable findings and that the discussion should be continued.

Why are literature reviews important?

Literature reviews constantly feed new research, that constantly feeds literature reviews…and we could go on and on. The fact is, one acts like a force over the other and this is what makes science, as a global discipline, constantly develop and evolve. As a scientist, writing a literature review can be very beneficial to your career, and set you apart from the expert elite in your field of interest. But it also can be an overwhelming task, so don’t hesitate in contacting Elsevier for text editing services, either for profound edition or just a last revision. We guarantee the very highest standards. You can also save time by letting us suggest and make the necessary amendments to your manuscript, so that it fits the structural pattern of a literature review. Who knows how many worldwide researchers you will impact with your next perfectly written literature review.

Know more: How to Find a Gap in Research .

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• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

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To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically evaluate: mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

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A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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Conducting a literature review: why do a literature review, why do a literature review.

• How To Find "The Literature"
• Found it -- Now What?

Besides the obvious reason for students -- because it is assigned! -- a literature review helps you explore the research that has come before you, to see how your research question has (or has not) already been addressed.

You identify:

• core research in the field
• experts in the subject area
• methodology you may want to use (or avoid)
• gaps in knowledge -- or where your research would fit in

It Also Helps You:

• Publish and share your findings
• Justify requests for grants and other funding
• Identify best practices to inform practice
• Set wider context for a program evaluation
• Compile information to support community organizing

Great brief overview, from NCSU

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• UConn Library
• Literature Review: The What, Why and How-to Guide
• Introduction

Literature Review: The What, Why and How-to Guide — Introduction

• Getting Started
• How to Pick a Topic
• Strategies to Find Sources
• Evaluating Sources & Lit. Reviews
• Tips for Writing Literature Reviews
• Writing Literature Review: Useful Sites
• Citation Resources
• Other Academic Writings

What are Literature Reviews?

So, what is a literature review? "A literature review is an account of what has been published on a topic by accredited scholars and researchers. In writing the literature review, your purpose is to convey to your reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. As a piece of writing, the literature review must be defined by a guiding concept (e.g., your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries." Taylor, D.  The literature review: A few tips on conducting it . University of Toronto Health Sciences Writing Centre.

Goals of Literature Reviews

What are the goals of creating a Literature Review?  A literature could be written to accomplish different aims:

• To develop a theory or evaluate an existing theory
• To summarize the historical or existing state of a research topic
• Identify a problem in a field of research 

Baumeister, R. F., & Leary, M. R. (1997). Writing narrative literature reviews .  Review of General Psychology , 1 (3), 311-320.

What kinds of sources require a Literature Review?

• A research paper assigned in a course
• A thesis or dissertation
• A grant proposal
• An article intended for publication in a journal

All these instances require you to collect what has been written about your research topic so that you can demonstrate how your own research sheds new light on the topic.

Types of Literature Reviews

What kinds of literature reviews are written?

Narrative review: The purpose of this type of review is to describe the current state of the research on a specific topic/research and to offer a critical analysis of the literature reviewed. Studies are grouped by research/theoretical categories, and themes and trends, strengths and weakness, and gaps are identified. The review ends with a conclusion section which summarizes the findings regarding the state of the research of the specific study, the gaps identify and if applicable, explains how the author's research will address gaps identify in the review and expand the knowledge on the topic reviewed.

• Example : Predictors and Outcomes of U.S. Quality Maternity Leave: A Review and Conceptual Framework:  10.1177/08948453211037398  

Systematic review : "The authors of a systematic review use a specific procedure to search the research literature, select the studies to include in their review, and critically evaluate the studies they find." (p. 139). Nelson, L. K. (2013). Research in Communication Sciences and Disorders . Plural Publishing.

• Example : The effect of leave policies on increasing fertility: a systematic review:  10.1057/s41599-022-01270-w

Meta-analysis : "Meta-analysis is a method of reviewing research findings in a quantitative fashion by transforming the data from individual studies into what is called an effect size and then pooling and analyzing this information. The basic goal in meta-analysis is to explain why different outcomes have occurred in different studies." (p. 197). Roberts, M. C., & Ilardi, S. S. (2003). Handbook of Research Methods in Clinical Psychology . Blackwell Publishing.

• Example : Employment Instability and Fertility in Europe: A Meta-Analysis:  10.1215/00703370-9164737

Meta-synthesis : "Qualitative meta-synthesis is a type of qualitative study that uses as data the findings from other qualitative studies linked by the same or related topic." (p.312). Zimmer, L. (2006). Qualitative meta-synthesis: A question of dialoguing with texts .  Journal of Advanced Nursing , 53 (3), 311-318.

• Example : Women’s perspectives on career successes and barriers: A qualitative meta-synthesis:  10.1177/05390184221113735

Literature Reviews in the Health Sciences

• UConn Health subject guide on systematic reviews Explanation of the different review types used in health sciences literature as well as tools to help you find the right review type
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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

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What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

APA7 Style resources

APA Style Blog - for those harder to find answers

1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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What is a Literature Review?

A literature or narrative review is a comprehensive review and analysis of the published literature on a specific topic or research question. The literature that is reviewed contains: books, articles, academic articles, conference proceedings, association papers, and dissertations. It contains the most pertinent studies and points to important past and current research and practices. It provides background and context, and shows how your research will contribute to the field. 

A literature review should: 

• Provide a comprehensive and updated review of the literature;
• Explain why this review has taken place;
• Articulate a position or hypothesis;
• Acknowledge and account for conflicting and corroborating points of view

From  S age Research Methods

Purpose of a Literature Review

A literature review can be written as an introduction to a study to:

• Demonstrate how a study fills a gap in research
• Compare a study with other research that's been done

Or it can be a separate work (a research article on its own) which:

• Organizes or describes a topic
• Describes variables within a particular issue/problem

Limitations of a Literature Review

Some of the limitations of a literature review are:

• It's a snapshot in time. Unlike other reviews, this one has beginning, a middle and an end. There may be future developments that could make your work less relevant.
• It may be too focused. Some niche studies may miss the bigger picture.
• It can be difficult to be comprehensive. There is no way to make sure all the literature on a topic was considered.
• It is easy to be biased if you stick to top tier journals. There may be other places where people are publishing exemplary research. Look to open access publications and conferences to reflect a more inclusive collection. Also, make sure to include opposing views (and not just supporting evidence).

Source: Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal, vol. 26, no. 2, June 2009, pp. 91–108. Wiley Online Library, doi:10.1111/j.1471-1842.2009.00848.x.

Meryl Brodsky : Communication and Information Studies

Hannah Chapman Tripp : Biology, Neuroscience

Carolyn Cunningham : Human Development & Family Sciences, Psychology, Sociology

Larayne Dallas : Engineering

Janelle Hedstrom : Special Education, Curriculum & Instruction, Ed Leadership & Policy ​

Susan Macicak : Linguistics

Imelda Vetter : Dell Medical School

For help in other subject areas, please see the guide to library specialists by subject .

Periodically, UT Libraries runs a workshop covering the basics and library support for literature reviews. While we try to offer these once per academic year, we find providing the recording to be helpful to community members who have missed the session. Following is the most recent recording of the workshop, Conducting a Literature Review. To view the recording, a UT login is required.

• October 26, 2022 recording
• Last Updated: Oct 26, 2022 2:49 PM
• URL: https://guides.lib.utexas.edu/literaturereviews

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Literature reviews, what is a literature review, learning more about how to do a literature review.

• Planning the Review
• The Research Question
• Choosing Where to Search
• Organizing the Review
• Writing the Review

A literature review is a review and synthesis of existing research on a topic or research question. A literature review is meant to analyze the scholarly literature, make connections across writings and identify strengths, weaknesses, trends, and missing conversations. A literature review should address different aspects of a topic as it relates to your research question. A literature review goes beyond a description or summary of the literature you have read. 

• Sage Research Methods Core Collection This link opens in a new window SAGE Research Methods supports research at all levels by providing material to guide users through every step of the research process. SAGE Research Methods is the ultimate methods library with more than 1000 books, reference works, journal articles, and instructional videos by world-leading academics from across the social sciences, including the largest collection of qualitative methods books available online from any scholarly publisher. – Publisher

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5 Reasons the Literature Review Is Crucial to Your Paper

3-minute read

• 8th November 2016

People often treat writing the literature review in an academic paper as a formality. Usually, this means simply listing various studies vaguely related to their work and leaving it at that.

But this overlooks how important the literature review is to a well-written experimental report or research paper. As such, we thought we’d take a moment to go over what a literature review should do and why you should give it the attention it deserves.

What Is a Literature Review?

Common in the social and physical sciences, but also sometimes required in the humanities, a literature review is a summary of past research in your subject area.

Sometimes this is a standalone investigation of how an idea or field of inquiry has developed over time. However, more usually it’s the part of an academic paper, thesis or dissertation that sets out the background against which a study takes place.

There are several reasons why we do this.

Reason #1: To Demonstrate Understanding

In a college paper, you can use a literature review to demonstrate your understanding of the subject matter. This means identifying, summarizing and critically assessing past research that is relevant to your own work.

Reason #2: To Justify Your Research

The literature review also plays a big role in justifying your study and setting your research question . This is because examining past research allows you to identify gaps in the literature, which you can then attempt to fill or address with your own work.

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Reason #3: Setting a Theoretical Framework

It can help to think of the literature review as the foundations for your study, since the rest of your work will build upon the ideas and existing research you discuss therein.

A crucial part of this is formulating a theoretical framework , which comprises the concepts and theories that your work is based upon and against which its success will be judged.

Reason #4: Developing a Methodology

Conducting a literature review before beginning research also lets you see how similar studies have been conducted in the past. By examining the strengths and weaknesses of existing research, you can thus make sure you adopt the most appropriate methods, data sources and analytical techniques for your own work.

Reason #5: To Support Your Own Findings

The significance of any results you achieve will depend to some extent on how they compare to those reported in the existing literature. When you come to write up your findings, your literature review will therefore provide a crucial point of reference.

If your results replicate past research, for instance, you can say that your work supports existing theories. If your results are different, though, you’ll need to discuss why and whether the difference is important.

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Conducting a Literature Review

Benefits of conducting a literature review.

• Steps in Conducting a Literature Review
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• Literature Review Tutorial by American University Library
• The Literature Review: A Few Tips On Conducting It by University of Toronto
• Write a Literature Review by UC Santa Cruz University Library

While there might be many reasons for conducting a literature review, following are four key outcomes of doing the review.

Assessment of the current state of research on a topic . This is probably the most obvious value of the literature review. Once a researcher has determined an area to work with for a research project, a search of relevant information sources will help determine what is already known about the topic and how extensively the topic has already been researched.

Identification of the experts on a particular topic . One of the additional benefits derived from doing the literature review is that it will quickly reveal which researchers have written the most on a particular topic and are, therefore, probably the experts on the topic. Someone who has written twenty articles on a topic or on related topics is more than likely more knowledgeable than someone who has written a single article. This same writer will likely turn up as a reference in most of the other articles written on the same topic. From the number of articles written by the author and the number of times the writer has been cited by other authors, a researcher will be able to assume that the particular author is an expert in the area and, thus, a key resource for consultation in the current research to be undertaken.

Identification of key questions about a topic that need further research . In many cases a researcher may discover new angles that need further exploration by reviewing what has already been written on a topic. For example, research may suggest that listening to music while studying might lead to better retention of ideas, but the research might not have assessed whether a particular style of music is more beneficial than another. A researcher who is interested in pursuing this topic would then do well to follow up existing studies with a new study, based on previous research, that tries to identify which styles of music are most beneficial to retention.

Determination of methodologies used in past studies of the same or similar topics.  It is often useful to review the types of studies that previous researchers have launched as a means of determining what approaches might be of most benefit in further developing a topic. By the same token, a review of previously conducted studies might lend itself to researchers determining a new angle for approaching research.

Upon completion of the literature review, a researcher should have a solid foundation of knowledge in the area and a good feel for the direction any new research should take. Should any additional questions arise during the course of the research, the researcher will know which experts to consult in order to quickly clear up those questions.

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Why Is Literature Review Important? (3 Benefits Explained)

by  Antony W

January 21, 2023

Every research project needs a literature review. And while it’s one of the most challenging parts of the assignment, in part because of the intensity of the research involved, it’s by far the most important section of a research paper.

Many students fail to write comprehensive literature reviews because they see the assignment as a formality.

For the most part, they’ll vaguely create a list of existing studies and consider the assignment complete. But such an approach overlooks why a literature review is important.

We need to take a step back and look beyond the definition of a literature review.

In particular, the goal of this guide is to help you explore the significance of the review of the existing literature.

Once you understand the role that literature reviews play in research projects, you’ll give the assignment the full attention that it deserves.

Key Takeaways

Writing a literature review is important for the following reasons:

• It demonstrates that you understand the issue you’re investigating.
• A literature review allows you to develop a more theoretical framework for your research. 
• It justifies your research and shows the gaps present in the current literature.

Get Literature Review Writing Help

Do you find the workload involved in writing a literature review for your thesis, research paper, or standalone project overwhelming? We understand how involving the writing process can be, and we are here to help you with writing if you currently feel stuck.

You can hire a  professional literature review writer   from Help for Assessment to get the writing done for you. Whether you have a flexible deadline or the submission date for the literature is almost due, you can count on our team to help you get the paper done fast. 

What is a Literature Review?

A literature review is a study of the already existing research in a given area of study.

While it’s common in physical and social sciences, instructors may also request student to complete the assignment within the humanities space.

The review can be a standalone project or a part of an academic assignment.

If your professor or instructor asks you to write the review as a standalone project, your focus will be on exploring how a specific field of inquiry has developed over the course of time.

In the case where you have to include the review as part of your academic paper, the goal will be to set the background for the topic (or issue) you’re currently investigating.

How is Literature Review Different from an Essay?

In an education setting whether students are used to writing tons of essays every month, it’s likely for many to wonder whether an essay could be the same as a literature review.

While a literature review and an essay both require research before writing, there are a number of differences between them that you need to know.

Types of Literature Review

We’ll look at the significance of a literature review in a moment.

For now let’s look at the types of literature reviews that your instructor may ask you to write.

As of this writing, there are 6 types of reviews that you need to know about. These are:

1. Argumentative Review

Examines a literature review with the intention to support or refuse an argument, with the aim being to develop a body of literature that can establish a contrarian point of view.

2. Integrative Literature Review

This type of review critiques and synthesizes related literature to generate a new framework and perspective on a topic.

Researchers have to address identical and/or related hypotheses or research problems to comply with research standards with regards to replication, vigor, and clarity.

3. Historical Literature

The focus of the review is to examine research within a given period, and usually starts from the time a research problem or issue emerged.

Then, you have to trace its evolution throughout the suggested timeframe within the scholarship of that particular discipline.

4. Methodological Literature Review

The focus shifts from what someone said to how they ended up saying what they said.

Since the focus here is on the method of analysis, methodological reviews gives a better framework that help one to understand exactly how a researcher draws their conclusion from a wide range of knowledge.

5. Systematic Literature

A systematic review focuses on the existing evidence related to a specific research question.

You will need to use a pre-specified and standardized approach to identify, evaluate, and appraise research, not to mention collect, analyze, and report data collected from the review.

Understand that the goal of a systematic review is to evaluate, summarize, and document research that focuses on a specific (or clearly defined) research problem.

6. Theoretical Literature Review

Theoretical review focuses on examining theories that resulted from an issue, a concept, or a situation.

It’s through this type of review that a researcher can easily establish the kind of theories that already formulated, the degree to what researchers have investigated them, and the relationship between them.

It’s through theoretical review that one can develop new hypotheses for testing and can therefore help to determine what theories aren’t sufficient to explain emerging research problems.

Why Is Literature Review Important?

Now that you know the difference between an essay and a review as well as the different types of literature review, it’s important to look at why it’s important to examine existing literature in your research.

There are a number of reasons why instructors ask you to write a review , and they’re as follow:

1. Demonstrate a Clear Understanding of the Subject

Writing a literature review demonstrates that you have a clear understanding of the subject you’re investigating.

It also means that you can easily identify, evaluate, and summarize existing research that’s relevant to your work. 

2. Justify Your Research

There’s more to writing a research paper than just identifying topic and generating your research question from it.

You also have to go as far as to justify your research, and the only way to do that is by including a literature review in your work.

It’s important to understand that looking at past research is the only way to identify gaps that exist in the current literature.

That can go a long way to help fill in the gap by addressing them in your own research work.

3. Helps to Set a Resourceful Theoretical Framework

Because a research paper assignment builds up on the ideas of already existing research, doing a literature review can help you to set a resourceful theoretical framework on which to base your study.

The theoretical framework will include concepts and theories that you will base your research on. And keep in mind that it’s this framework that professors will use to judge the overall quality of your work. 

Frequently Asked Questions

1. what are the benefits of literature review in research.

A literature review in research allows you to discover exiting knowledge in your field and the boundaries and limitations that exists within that field.

Moreover, doing a review of existing literature helps you to understand the theories that drive an area of investigation, making it easy for you to place your research question  into proper context. 

2. What is the Effect of a Good Literature Review?

In addition to providing context, reducing research redundancy, and informing methodology, a well-written literature review can maximize relevance, enhance originality, and ensure professional standards in writing.

3. What is a Strength of a Literature Review?

The strength of a literature review is the ability to improve your information seeking skills and enhancing your knowledge about the topic under investigation.

As you can see, a review is quite a significant part of a research project, so you should treat it with the seriousness that it deserves.

At the end of the day, you want to create a good connection between you and your readers, and the best way to do that is to pack just as much value as you can in your literature review project.

About the author 

Antony W is a professional writer and coach at Help for Assessment. He spends countless hours every day researching and writing great content filled with expert advice on how to write engaging essays, research papers, and assignments.

BENEFITS OF PALLIATIVE CARE IN ADULTS WITH A DIAGNOSIS OF HEART FAILURE: AN EXPLORATORY LITERATURE REVIEW

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Introduction: Heart Failure is a clinical syndrome characterized by a series of symptoms such as dyspnea, orthopnea and edema in the lower limbs. This pathology continues to have a high prevalence despite advances in pharmacotherapy and device therapy and given that it is a pathology that significantly impairs the quality of life of patients, the implementation of care is of vital importance. However, these are underused due to lack of knowledge on the part of health personnel and also due to poor implementation in the different health providers. Objective: An exploratory review of the literature was carried out regarding the benefits of palliative care in patients with advanced heart failure, in order to synthesize the available and updated evidence. Methodology: Searched for articles published from 2017 to 2022 related to palliative care in patients with heart failure and using the PRISMA 2020 methodology for this study. This inquiry of articles was carried out in the following databases: UpToDate, PubMed, MESH, PMC (US National Library of Medicine National Institutes of health). Results: A total of 5 articles were obtained, from which they concluded that palliative care has a positive impact on the quality of life of patients with heart failure, there was a lower rate of hospital readmissions, improvements in physical, psychological and existential.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

This study did not receive any funding

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I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Data Availability

All data produced in the present work are contained in the manuscript

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Early age at menarche and history of sexually transmitted infections significantly predict cervical cancer screening uptake among women aged 25–49 years: evidence from the 2021 Côte d’Ivoire demographic and health survey

• Joshua Okyere 1 , 2 ,
• Castro Ayebeng 1 &
• Kwamena Sekyi Dickson 1  

BMC Health Services Research volume  24 , Article number:  423 ( 2024 ) Cite this article

Metrics details

Introduction

Cervical cancer is the second dominant type of cancer among Ivorian women with an estimated age-standardised incidence and mortality rate of 31.2 cases and 22.8 deaths per 100,000 women in 2020, respectively. The Ivorian government through its Ministry of Health implemented the National Cancer Control Programme (NCCP) in 2003 with the aim of improving the prevention, early detection and treatment of cancers in Côte d’Ivoire. Yet, there is a low uptake of CCS (1.2%). Thus, making CCS uptake an important public health concern in the country. Understanding of the extent to which reproductive factors predict CCS uptake is limited in literature. This study aimed to investigate reproductive factors as a predictor of women’s uptake of CCS in Côte d’Ivoire.

Data from the 2021 Côte d’Ivoire Demographic and Health Survey. A sample of 9,078 women aged 25–49 years were analyzed. The outcome variable was CCS uptake while other variables considered included age at menarche, history of STI, sexual debut, parity, age, educational level, wealth index, health insurance, place of residence, and media exposure. A multivariable logistic regression model was fitted to examine the association between the outcome of interest and predictors at 95% confidence interval.

Approximately, 7.52% of women aged 25–49 years had ever undergone testing for cervical cancer by a healthcare provider. Early menarche was associated with lower odds of CCS uptake [AOR = 0.78; CI = 0.65–0.95]. Compared to those who had no STI, women with a history of STI were more likely to screen for cervical cancer [AOR = 2.63; CI = 2.02–3.42]. Increasing age, higher educational attainment, having health insurance, and being exposed to media were significantly associated with CCS uptake.

In Cote d’Ivoire, age at menarche and STI history constitute reproductive factors that were significantly associated with women’s uptake of CCS. It is imperative for public policy to focus on increasing CCS in these higher-risk women (i.e., women who experienced early menarche, women with early sexual debut and higher parity) through increased sensitization on cervical cancer risk factors.

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Globally, there is ubiquitous consensus that cervical cancer is a serious public health concern [ 1 ]. The recognition of cervical cancer as a public health concern was highlighted in the World Health Organisation (WHO) Director’s call to eliminate this disease [ 2 ]. Cancer of the cervix is the fourth most common cancer among women worldwide, with an estimated 604,000 new cases and 342,000 deaths reported in 2020 [ 3 ]. Within the sub-Saharan African (SSA) context, cervical cancer remains the second most reported cancer among women [ 4 ].

The situation in Côte d’Ivoire is not different from what has been found in SSA. Available evidence indicates that cervical cancer is the second dominant type of cancer among Ivorian women with an estimated age-standardised incidence and mortality rate of 31.2 cases and 22.8 deaths per 100,000 women in 2020, respectively [ 5 , 6 ]. To address the high incidence and mortality attributable to cervical cancer, the Ivorian government through its Ministry of Health implemented the National Cancer Control Programme (NCCP) in 2003 with the aim of improving the prevention, early detection and treatment of cancers in Côte d’Ivoire [ 7 ]. A core tenet of the NCCP was to improve women’s utilization of cervical cancer screening (CCS) methods including visual inspection with acetic acid and cryotherapy [ 6 , 7 ]. Consequently, registered health care facilities in both government and private sector, as well as HIV integrated facilities offer CCS services to women aged 25–55 years by adopting a ‘see-and-treat’ approach [ 7 ]. Both the NCCP and the American Cancer Society recommend that women initiate CCS at age 25 years [ 7 , 8 ].

Despite the implementation of the NCCP, the uptake of CCS remains unacceptably low among Ivorian women. A study by Boni et al. [ 9 ] revealed that only 1.2% of women in urban areas of Abidjan had undergone screening for cervical cancer. The low uptake of CCS in Côte d’Ivoire have been attributed to unawareness of CCS, negligence, apprehension regarding positive test results, and concerns about additional costs [ 9 ]. Additionally, factors such as age, educational level, wealth status, health insurance coverage, and exposure to the media have been found to significantly predict women’s uptake of CCS [ 6 , 9 , 10 ]. Furthermore, CCS in Côte d’Ivoire is not free; it comes at a cost that tends to be a barrier to screening uptake [ 6 ]. However, the current body of literature on CCS uptake in Côte d’Ivoire is silent about the role of reproductive factors in predicting CCS uptake among the general women population.

In the context of this study, reproductive factors include age at menarche, sexual debut, parity, and history of sexually transmitted infections (STIs). Extant literature has documented the intricate relationship between reproductive factors and cervical cancer risk. For instance, Pillai et al. [ 11 ] reported in their study that Chlamydia infections significantly increase women’s risk of cervical cancer. Another study conducted in China revealed that lower parity was significantly associated with lower odds of developing cervical cancer while concurrent reproductive tract infections exacerbated the risk of cervical cancer [ 12 ]. Similarly, in a case-control study conducted among persons living with cervical cancer, it was revealed that early menarche, early sexual debut (i.e., < 18 years), and high parity (i.e., 3–5 births) was associated with a higher risk of cervical cancer [ 13 ]. As a public health concern, it is imperative to gain understanding of how high-risk reproductive factors are associated with CCS uptake in Côte D’Ivoire. To the best of our knowledge, there is currently no published research in Côte d’Ivoire that has investigated the extent to which reproductive factors are associated with CCS uptake. This signifies a critical knowledge gap that must be filled. This study aimed to investigate reproductive factors as a predictor of the uptake of CCS among women aged 25–49 years in Côte d’Ivoire.

Study design and data source

We utilized data from the 2021 Côte d’Ivoire Demographic and Health Survey (DHS), which is part of the broader global DHS series. Specifically, the individual recode file (i.e., CIIR81FL) was used. The primary objective of DHS is to collect nationally representative data from developing countries, with a specific focus on women aged 15 to 49 years [ 14 ]. To ensure comprehensive national representation, the DHS employed a two-stage sampling design and computed corresponding sampling weights [ 14 ].

At the first stage of the sampling, 539 clusters, 261 of which are located in the in urban areas and 278 in rural areas were drawn for survey [ 15 ]. A sample of 15,092 households (7,308 urban and 7,784 rural) was chosen, with 28 households selected per cluster [ 15 ]. The clusters were selected systematically, with the probability of selection proportional to their household size. These clusters were initially established during the census mapping database conducted in 2019 by the National Institute of Statistics as part of the preparations for the 2021 Population and Housing Census (RGPH) [ 15 ]. Data collection was conducted from September 8 to December 30, 2021, by 196 investigating officers organized into 24 teams [ 15 ]. All 539 clusters were thoroughly investigated, resulting in the selection of a total of 15,093 households, out of which 14,873 were occupied [ 15 ]. Among these occupied households, 14,766 were successfully surveyed, indicating a 99% response rate. Details of the DHS can be found here: https://www.dhsprogram.com/pubs/pdf/FR385/FR385.pdf .

Study population

As earlier indicated, the 2021 Côte d’Ivoire DHS surveyed a total of 14,766 women aged 15–49 years. However, for this study, we excluded women younger than 25 years as per the CCS recommendations [ 7 , 8 ]. Also, because we were interested in sexual debut and age at menarche, we excluded all women who had never had sex, those who had never menstruated, or did not know the age which they first menstruated. Consequently, our study population was women aged 25–49 years, who had complete data on all variables of interest in this study (see Fig.  1 ).

Outcome variable

The dependent variable was CCS utilization which was generated from the question, “Have you ever been tested for cervical cancer by a healthcare provider?”. The responses to this question were no, yes, and don’t know. However, we dropped “don’t know” to have a binary response of “0 = No” and “1 = Yes”.

Key explanatory variables

Our key explanatory variable was reproductive factors. This included age at menarche, sexual debut, parity, and history of STIs in the last 12 months. Age at menarche was coded as “before age 15” and “at 15 years or older”. Sexual debut was coded as “before age 18” and “at 18 years or older”, while parity was coded as nulliparous, uniparous and multiparous. History of STIs in the last 12 months had the responses of “Yes” and “No”.

Informed by a plethora of extant literature [ 6 , 9 , 10 ], a total of eight variables were selected as covariates. This encompassed age, educational level, wealth index, place of residence, frequency of reading newspapers/magazines, frequency of listening to radio, frequency of watching television, health insurance coverage, and marital status (see Supplementary File 1).

Statistical analyses

The total sample from the data was 14,877. However, after dropping the sample aged 15–24 years, we had a remaining sample of 9,078 (see Fig.  1 ). We initiated the analysis by applying the STATA weighting the data using the sample weight (v005). Subsequently, we conducted a cross-tabulation to examine the distribution of all sample variables. To assess whether the proportional distribution significantly differed, we computed Pearson’s chi-square ( X 2 ) test.

Next, we employed a bivariable logistic regression model to explore the association between the respective reproductive factors and CCS uptake. The results from the bivariable analysis were presented in terms of odds ratios at a 95% confidence interval. Following the bivariable analysis, we performed a multivariable logistic regression analysis, aiming to adjust for the influences of covariates. The outcomes of the multivariable analysis were presented in the form of adjusted odds ratios and their associated 95% confidence intervals. All these statistical analyses were conducted using STATA version 14 (StataCorp, College Station, TX, USA). We relied on the Akaike information criterion (AIC) to select the best-fit model. In both models, we computed the AIC. The model with the least AIC was selected as the best-fit model, which in this case was Model II.

Flowchart of the sampling procedure

Distribution of CCS uptake across the various explanatory variables

Table  1 shows the distribution of CCS uptake across the various variables. The results indicate that only 7.52% of women aged 25–49 years had ever undergone testing for cervical cancer by a healthcare provider. Regarding the reproductive factors, the proportion of CCS uptake was significantly high among those who menstruated at age 15 or older (8.05%), those who had an STI in the last 12 months (13.55%), those who had their first sex at age 18 or older (11.02%), and among uniparous women (13.96%). Higher proportion of CCS uptake was reported among women aged 45–49 years (9.56%), those residing in urban areas (10.75%), and women with higher educational attainment (31.20%). Also, a higher uptake of CCS was found among women who read the newspaper at least once a week (21.41%), those who listened to the radio at least once a week (12.83%), and those who watched television at least once a week (10.92%). The uptake of CCS was significantly high among women in the richest wealth index (18.21%) and those with health insurance coverage (27.97%).

Association between reproductive factors and CCS uptake among women

In Table  2 , we present the results from the bivariable and multivariable logistic regression. In the bivariable regression, all four reproductive factors were significant predictors of women’s uptake of cervical cancer screening (CCS). However, after adjusting for the covariates in Model II, two reproductive factors remained significant predictors. Early menarche was associated with lower odds of CCS uptake [AOR = 0.78; 95%CI = 0.64–0.95]. Conversely, compared to those who had no STIs, women with a history of STI were more likely to be screened for cervical cancer [AOR = 2.62; CI = 2.01–3.40]. Additionally, the covariates showed significant associations with CCS uptake: higher educational attainment [AOR = 3.31; CI = 2.26–4.85], older age [AOR = 2.01; CI = 1.43–2.81], belonging to the richest wealth index [AOR = 2.74; CI = 1.68–4.45], and having health insurance coverage [AOR = 2.60; CI = 1.98–3.41] were associated with higher CCS uptake. Moreover, listening to the radio at least once a week was significantly associated with a higher likelihood of CCS uptake compared to not listening to the radio at all [AOR = 1.48; CI = 1.16–1.89].

Efficient and systematic screening for precancerous lesions and early detection play a critical role in the prevention and treatment of cervical cancer. This study examined the association between reproductive factors (i.e., age at menarche, history of sexually transmitted infections, early initiation of sexual activity, and parity) and the uptake of CCS among Ivorian women aged 25–49 years. Indeed, the study reveals a significant association between reproductive factors including other covariates (such as education, age, exposure to mass media, wealth status, and health insurance coverage) and CCS uptake. Overall, we found that only 7.52% of the sampled population had ever been screened for cervical cancer. Similarly, low CCS uptake has been reported in other studies conducted in Tanzania [ 16 ] and Uganda [ 17 ] which found 6% and 4.8%, respectively. The observed prevalence is, however, higher when compared to Boni et al. [ 9 ] study that reported a prevalence of 1.2%. A probable reason for this difference is that Boni et al.’ study [ 9 ] focused only on urban areas of Abidjan while the present study provides a more nationally representative estimation of CCS uptake.

Age at menarche emerged as significant a predictor of women’s uptake of CCS. Our study indicates that women who experienced early menarche (i.e., before 15 years) were less likely to undergo screening for cervical cancer. This result is inconsistent with Sharma and Pattanshetty [ 13 ] whose study suggests that early menarche is a high-risk factor for cervical cancer, and thus, a potential factor in influencing CCS uptake. It is unclear what factors contribute to the observed association. Further research into the specific barriers faced by women with early menarche in accessing CCS could provide valuable insights for targeted interventions aimed at increasing screening uptake in this group.

The study showed a strong positive association between women’s history of sexually transmitted infections (STIs) and the likelihood of screening for cervical cancer. Women who had been diagnosed with any STIs within the last 12 months preceding the survey were 2.62 times more likely to undergo screening. Extant literature suggests that STIs such as chlamydia and human papillomavirus (HPV) increase the risks of cervical carcinogenesis [ 18 , 19 , 20 ]. We, therefore, postulate that healthcare providers would be more likely to suggest CCS to women who had tested positive for any STIs [ 21 ].

As expected, higher educational attainment was associated with a greater likelihood of CCS uptake. This finding aligns with a study conducted in Zimbabwe [ 22 ] where women with secondary and tertiary education were 9.4 and 59.4 times more likely to undergo screening, respectively, than those without any formal education. Women with a higher level of education are likely to possess a more comprehensive understanding of the significance of preventive measures like screening for cervical cancer. Consistent with previous studies conducted in Cameroon [ 10 ], Burkina Faso [ 23 ] and South Africa [ 24 ], we found a pattern of increasing screening uptake as age increases. Available evidence suggests that the risks of non-communicable diseases including cervical cancer increase with ageing [ 25 , 26 ]. Therefore, older women of reproductive age may perceive themselves as being at a higher risk of cervical cancer than younger women. Hence, informing their screening uptake behavior. It is also possible that as age progresses women would have had more opportunity to participate in CCS in their lifetime compared to younger women.

Congruent with existing literature [ 27 , 28 , 29 ], the study demonstrated that being exposed to the mass media such as newspapers/magazines, and the radio at least once a week had a positive influence on women’s screening behavior. The result epitomizes the role of the media as a channel for the dissemination of health education messages, encompassing the advantages of participating in adopting preventive health behaviors, including CCS uptake.

We also observed an increased odds of CCS uptake among women of higher wealth status compared to those in the poorest wealth status. This finding aligns with the outcomes of similar research conducted in Cameroon [ 10 ] and Kenya [ 29 ]. It suggests that economic factors significantly influence women’s access to preventive healthcare services like CCS. Women with greater financial resources may have more opportunities to access and afford healthcare, including screenings. This assertion is further corroborated by our findings that women who had health insurance coverage were more likely to get screened for cervical cancer than those who did not have health insurance. Similar findings have been reported in a South African study [ 30 ] that found health insurance coverage to be associated with a 60.3% higher uptake of CCS. Accessing screening for cervical cancer comes with both direct and indirect costs (e.g., transportation costs). However, health insurance coverage offsets the direct cost and reduces the financial barriers to screening uptake.

Implications for policy and practice

Based on the findings from the study, it is imperative for the Ministry of Health and all healthcare facilities providing CCS services to prioritize the reproductive factors of women as a key indicator for screening. With the exception of a history of STI, women at higher risk for cervical cancer (i.e., women with higher parity, early sexual debut, and early menarche) are not more likely to be screened when accounting for socio-demographic and economic variables. Priority should be given to targeting women who exhibit factors associated with higher risk of cervical cancer but are less likely to undergo screening, such as higher parity, early sexual debut, and early menarche. Our study results substantiate the notion that the implementation of a universal health insurance scheme aimed at ensuring equitable access to healthcare can significantly augment the likelihood of women’s utilization of CCS. The result from this study also highlights how important the media can be leveraged to disseminate information and encourage Ivorian women to undergo screening for cervical cancer. One study [ 31 ] has shown that the adoption of entertainment-education approaches such as the use of soap-operas are effective tools for raising women’s awareness about cervical cancer, risk factors, and the need for screening. Similar approaches can be adopted in Cote d’Ivoire to facilitate the leverage of the media to enhance CCS uptake. Countries like Ghana have what is known as the School Health Education Programme (SHEP) where health practitioners are assigned to schools as SHEP coordinators [ 32 ]. They are responsible for health promotion and health education at various levels. Cote d’Ivoire’s Ministry of Health can adopt such initiative to ensure that in-school women are reached with CCS information while working to on the side to reach those currently not in school.

Strengths and limitations of the study

This study boasts several strengths that enhance its validity. We employed a secondary analysis of the recent Demographic and Health survey data, which provides a representative sample of Ivorian women, enhancing the generalizability of our findings. The comprehensive analysis of various reproductive factors by adjusting for other relevant socio-demographic and economic determinants in relation to CCS contributes to a more holistic understanding of this critical public health issue. Additionally, the alignment of our results with existing literature from different regions and countries enhances the credibility and robustness of our findings. However, this study has certain limitations to consider when interpreting the findings. Firstly, the data utilized is cross-sectional, which limits our ability to establish causal relationships between the variables studied. Furthermore, the data relies on self-reported information, which may introduce recall bias or social desirability bias. Also, the study lacks qualitative insights that could provide a deeper understanding of the reasons behind the observed associations, including the influence of some cultural norms and values on screening behavior.

In Cote d’Ivoire, age at menarche and STI history constitute reproductive factors that were significantly associated with women’s uptake of CCS. It is imperative for public policy to focus on increasing CCS in these higher risk women (i.e., women who experienced early menarche, women with early sexual debut and higher parity) through increased sensitization on cervical cancer risk factors. Also, the Ivorian government and the Ministry of Health should consider expanding their health insurance scheme to cover the cost of CCS. This is likely to significantly narrow the disparities posed by wealth inequalities and non-health insurance coverage.

Data availability

The datasets generated and/or analysed during the current study are available in the Measure DHS repository: http://dhsprogram.com/data/available-datasets.cfm .

Abbreviations

Adjusted Odds Ratio

Confidence Interval

Cervical Cancer Screening

Demographic and Health Survey

National Cancer Control Programme

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Okyere, J., Ayebeng, C. & Dickson, K.S. Early age at menarche and history of sexually transmitted infections significantly predict cervical cancer screening uptake among women aged 25–49 years: evidence from the 2021 Côte d’Ivoire demographic and health survey. BMC Health Serv Res 24 , 423 (2024). https://doi.org/10.1186/s12913-024-10881-9

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• Published: 28 March 2024

New water accounting reveals why the Colorado River no longer reaches the sea

• Brian D. Richter   ORCID: orcid.org/0000-0001-7216-1397 1 , 2 ,
• Gambhir Lamsal   ORCID: orcid.org/0000-0002-2593-8949 3 ,
• Landon Marston   ORCID: orcid.org/0000-0001-9116-1691 3 ,
• Sameer Dhakal   ORCID: orcid.org/0000-0003-4941-1559 3 ,
• Laljeet Singh Sangha   ORCID: orcid.org/0000-0002-0986-1785 4 ,
• Richard R. Rushforth 4 ,
• Dongyang Wei   ORCID: orcid.org/0000-0003-0384-4340 5 ,
• Benjamin L. Ruddell 4 ,
• Kyle Frankel Davis   ORCID: orcid.org/0000-0003-4504-1407 5 , 6 ,
• Astrid Hernandez-Cruz   ORCID: orcid.org/0000-0003-0776-5105 7 ,
• Samuel Sandoval-Solis 8 &
• John C. Schmidt 9  

Communications Earth & Environment volume  5 , Article number:  134 ( 2024 ) Cite this article

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Persistent overuse of water supplies from the Colorado River during recent decades has substantially depleted large storage reservoirs and triggered mandatory cutbacks in water use. The river holds critical importance to more than 40 million people and more than two million hectares of cropland. Therefore, a full accounting of where the river’s water goes en route to its delta is necessary. Detailed knowledge of how and where the river’s water is used can aid design of strategies and plans for bringing water use into balance with available supplies. Here we apply authoritative primary data sources and modeled crop and riparian/wetland evapotranspiration estimates to compile a water budget based on average consumptive water use during 2000–2019. Overall water consumption includes both direct human uses in the municipal, commercial, industrial, and agricultural sectors, as well as indirect water losses to reservoir evaporation and water consumed through riparian/wetland evapotranspiration. Irrigated agriculture is responsible for 74% of direct human uses and 52% of overall water consumption. Water consumed for agriculture amounts to three times all other direct uses combined. Cattle feed crops including alfalfa and other grass hays account for 46% of all direct water consumption.

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Introduction

Barely a trickle of water is left of the iconic Colorado River of the American Southwest as it approaches its outlet in the Gulf of California in Mexico after watering many cities and farms along its 2330-kilometer course. There were a few years in the 1980s in which enormous snowfall in the Rocky Mountains produced a deluge of spring snowmelt runoff capable of escaping full capture for human uses, but for most of the past 60 years the river’s water has been fully consumed before reaching its delta 1 , 2 . In fact, the river was overconsumed (i.e., total annual water consumption exceeding runoff supplies) in 16 of 21 years during 2000–2020 3 , requiring large withdrawals of water stored in Lake Mead and Lake Powell to accommodate the deficits. An average annual overdraft of 10% during this period 2 caused these reservoirs– the two largest in the US – to drop to three-quarters empty by the end of 2022 4 , triggering urgent policy decisions on where to cut consumption.

Despite the river’s importance to more than 40 million people and more than two million hectares (>5 million acres) of cropland—producing most of the vegetable produce for American and Canadian plates in wintertime and also feeding many additional people worldwide via exports—a full sectoral and crop-specific accounting of where all that water goes en route to its delta has never been attempted, until now. Detailed knowledge of how and where the river’s water is used can aid design of strategies and plans for bringing water use into balance with available supplies.

There are interesting historical reasons to explain why this full water budget accounting has not been accomplished previously, beginning a full century ago when the apportionment of rights to use the river’s water within the United States was inscribed into the Colorado River Compact of 1922 5 . That Compact was ambiguous and confusing in its allocation of water inflowing to the Colorado River from the Gila River basin in New Mexico and Arizona 6 , even though it accounts for 24% of the drainage area of the Colorado River Basin (Fig.  1 ). Because of intense disagreements over the rights to the Gila and other tributaries entering the Colorado River downstream of the Grand Canyon, the Compact negotiators decided to leave the allocation of those waters rights to a later time so that the Compact could proceed 6 . Arizona’s formal rights to the Gila and other Arizona tributaries were finally affirmed in a US Supreme Court decision in 1963 that also specified the volumes of Colorado River water allocated to California, Arizona, and Nevada 7 . Because the rights to the Gila’s waters lie outside of the Compact allocations, the Gila has not been included in formal accounting of the Colorado River Basin water budget to date 8 . Additionally, the Compact did not specify how much water Mexico—at the river’s downstream end—should receive. Mexico’s share of the river was not formalized until 22 years later, in the 1944 international treaty on “Utilization of the Waters of the Colorado and Tijuana Rivers and of the Rio Grande” (1944 Water Treaty) 9 . As a result of these political circumstances, full accounting for direct water consumption at the sectoral level—in which water use is accounted according to categories such as municipal, industrial, commercial, or agricultural uses—has not previously been compiled for the Gila River basin’s water, and sectoral accounting for Mexico was not published until 2023 10 .

The physical boundary of the Colorado River Basin is outlined in black. Hatched areas outside of the basin boundary receive Colorado River water via inter-basin transfers (also known as ‘exports’). The Gila River basin is situated in the far southern portion of the CRB in Arizona, New Mexico, and Mexico. Map courtesy of Center for Colorado River Studies, Utah State University.

The US Bureau of Reclamation (“Reclamation”)—which owns and operates massive water infrastructure in the Colorado River Basin—has served as the primary accountant of Colorado River water. In 2012, the agency produced a “Colorado River Basin Water Supply and Demand Study” 8 that accounted for both the sectoral uses of water within the basin’s physical boundaries within the US as well as river water exported outside of the basin (Fig.  1 ). But Reclamation did not attempt to account for water generated from the Gila River basin because of that sub-basin’s exclusion from the Colorado River Compact, and it did not attempt to explain how water crossing the border into Mexico is used. The agency estimated riparian vegetation evapotranspiration for the lower Colorado River but not the remainder of the extensive river system. Richter et al. 11 published a water budget for the Colorado River that included sectoral and crop-specific water consumption but it too did not include water used in Mexico, nor reservoir evaporation or riparian evapotranspiration, and it did not account for water exported outside of the Colorado River Basin’s physical boundary as illustrated in Fig.  1 . Given that nearly one-fifth (19%) of the river’s water is exported from the basin or used in Mexico, and that the Gila is a major tributary to the Colorado, this incomplete accounting has led to inaccuracies and misinterpretations of “where the Colorado River’s water goes” and has created uncertainty in discussions based on the numbers. This paper provides fuller accounting of the fate of all river water during 2000–2019, including averaged annual consumption in each of the sub-basins including exports, consumption in major sectors of the economy, consumption in the production of specific types of crops, and water consumed by reservoir evaporation and riparian/wetland evapotranspiration.

Rising awareness of water overuse and prolonged drought has driven intensifying dialog among the seven US states sharing the basin’s waters as well as between the United States, Mexico, and 30 tribal nations within the US. Since 2000, six legal agreements affecting the US states and two international agreements with Mexico have had the effect of reducing water use from the Colorado River 7 :

In 2001, the US Secretary of the Interior issued a set of “Interim Surplus Guidelines” to reduce California’s water use by 14% to bring the state within its allocation as determined in the 1963 US Supreme Court case mentioned previously. A subsequent “Quantification Settlement Agreement” executed in 2003 spelled out details about how California was going to achieve the targeted reduction.

In 2007, the US Secretary of the Interior adopted a set of “Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead” that reduced water deliveries to Arizona and Nevada when Lake Mead drops to specified levels, with increasing cutbacks as levels decline.

In 2012, the US and Mexican federal governments signed an addendum to the 1944 Water Treaty known as Minute 319 that reduced deliveries to Mexico as Lake Mead elevations fall.

In 2017, the US and Mexican federal governments established a “Binational Water Scarcity Contingency Plan” as part of Minute 323 that provides for deeper cuts in deliveries to Mexico under specified low reservoir elevations in Lake Mead.i

In 2019, the three Lower Basin states and the US Secretary of the Interior agreed to commitments under the “Lower Basin Drought Contingency Plan” that further reduced water deliveries beyond the levels set in 2007 and added specifications for deeper cuts as Lake Mead drops to levels lower than anticipated in the 2007 Guidelines.

In 2023, the states of California, Arizona and Nevada committed to further reductions in water use through the year 2026 12 .

With each of the above agreements, overall water consumption has been reduced but many scientists assert that these reductions still fall substantially short of balancing consumptive use with 21st century water supplies 2 , 13 . With all of these agreements—excepting the Interim Surplus Guidelines of 2001—set to expire in 2026, management of the Colorado River’s binational water supply is now at a crucial point, emphasizing the need for comprehensive water budget accounting.

Our tabulation of the Colorado River’s full water consumption budget (Table  1 ) provides accounting for all direct human uses of water as either agricultural or MCI (municipal, commercial, industrial), as well as indirect losses of water to reservoir evaporation and evapotranspiration from riparian or wetland vegetation including in the Salton Sea and in a wetland in Mexico (Cienega de Santa Clara) that receives agricultural return flows from irrigated areas in Arizona. We explicitly note that all estimates represent consumptive use , resulting from the subtraction of return flows from total water withdrawals. Table  2 provides a summary based only on direct human uses and does not include indirect consumption of water. We have provided Tables  1 and 2 in English units in our Supplementary Information as Tables SI-1 and SI-2 . We have lumped municipal, commercial, and industrial (MCI) uses together because these sub-categories of consumption are not consistently differentiated within official water delivery data for cities utilizing Colorado River water. More detail on urban water use by cities dependent on the river is available in Richter 14 , among other studies.

We differentiated water consumption geographically using the ‘accounting units’ mapped in Fig.  2 , which are based on the Colorado River Basin map as revised by Schmidt 15 ; importantly, these accounting units align spatially with Reclamation’s accounting systems for the Upper Basin and Lower Basin as described in our Methods, thereby enabling readers accustomed to Reclamation’s water-use reports to easily comprehend our accounting. We have also accounted for all water consumed within the Colorado River Basin boundaries as well as water exported via inter-basin transfers. Water exported outside of the basin includes 47 individual inter-basin transfer systems (i.e., canals, pipelines, pumps) that in aggregate export ~12% of the river’s water. We note that the Imperial Irrigation District of southern California is often counted as a recipient of exported water, but we have followed the rationale of Schmidt 15 by including it as an interior part of the Lower Basin even though it receives its Colorado River water via the All American Canal (Fig.  2 ).

The water budget estimates presented in Tables  1 and 2 are summarized for each of the seven “accounting units” displayed here.

These results confirm previous findings that irrigated agriculture is the dominant consumer of Colorado River water. Irrigated agriculture accounts for 52% of overall consumption (Table  1 ; Figs.  3 and 4 ) and 74% of direct human consumption (Table  2 ) of water from the Colorado River Basin. As highlighted in Richter et al. 11 , cattle-feed crops (alfalfa and other hay) are the dominant water-consuming crops dependent upon irrigation water from the basin (Tables  1 and 2 ; Figs.  3 and 4 ). Those crops account for 32% of all water consumed from the basin, 46% of all direct water consumption, and 62% of all agricultural water consumed (Table  1 ; Fig.  3 ). The percentage of water consumed by irrigated crops is greatest in Mexico, where they account for 86% of all direct human uses (Table  2 ) and 80% of total water consumed (Table  1 ). Cattle-feed crops consume 90% of all water used by irrigated agriculture within the Upper Basin, where the consumed volume associated with these cattle-feed crops amounts to more than three times what is consumed for municipal, commercial, or industrial uses combined.

All estimates based on 2000–2019 averages. Both agriculture and MCI (municipal, commercial, and industrial) uses are herein referred to as “direct human uses.” “Indirect uses” include both reservoir evaporation as well as evapotranspiration by riparian/wetland vegetation.

Water consumed by each sector in the Colorado River Basin and sub-basins (including exports), based on 2000–2019 averages.

Another important finding is that a substantial volume of water (19%) is consumed in supporting the natural environment through riparian and wetland vegetation evapotranspiration along river courses. This analysis—made possible because of recent mapping of riparian vegetation in the Colorado River Basin 16 —is an important addition to the water budget of the Colorado River Basin, given that the only previous accounting for riparian vegetation consumption has limited to the mainstem of the Colorado River below Hoover Dam and does not include vegetation upstream of Hoover Dam nor vegetation along tributary rivers 17 . Given that many of these habitats and associated species have been lost or became imperiled due to river flow depletion 18 —including the river’s vast delta ecosystem in Mexico—an ecologically sustainable approach to water management would need to allow more water to remain in the river system to support riparian and aquatic ecosystems. Additionally, 11% of all water consumed in the Colorado River Basin is lost through evaporation from reservoirs.

It is also important to note a fairly high degree of inter-annual variability in each sector of water use; for example, the range of values portrayed for the four water budget sectors shown in Fig.  5 equates to 24–47% of their 20-year averages. Also notable is a decrease in water consumed in the Lower Basin between the years 2000 and 2019 for both the MCI (−38%) and agricultural sectors (−15%), which can in part be attributed to the policy agreements summarized previously that have mandated water-use reductions.

Inter-annual variability of water consumption within the Lower and Upper Basins, including water exported from these basins. The average (AVG) values shown are used in the water budgets detailed in Tables  1 and 2 .

The water accounting in Richter et al. 11 received a great deal of media attention including a front-page story in the New York Times 19 . These stories focused primarily on our conclusion that more than half (53%) of water consumed in the Colorado River Basin was attributable to cattle-feed crops (alfalfa and other hays) supporting beef and dairy production. However, that tabulation of the river’s water budget had notable shortcomings, as discussed previously. In this more complete accounting that includes Colorado River water exported outside of the basin’s physical boundary as well as indirect water consumption, we find that irrigated agriculture consumes half (52%) of all Colorado River Basin water, and the portion of direct consumption going to cattle-feed crops dropped from 53% as reported in Richter et al. 11 to 46% in this revised analysis.

These differences are explained by the fact that we now account for all exported water and also include indirect losses of water to reservoir evaporation and riparian/wetland evapotranspiration in our revised accounting, as well as improvements in our estimation of crop-water consumption. However, the punch line of our 2020 paper does not change fundamentally. Irrigated agriculture is the dominant consumer of water from the Colorado River, and 62% of agricultural water consumption goes to alfalfa and grass hay production.

Richter et al. 20 found that alfalfa and grass hay were the largest water consumers in 57% of all sub-basins across the western US, and their production is increasing in many western regions. Alfalfa is favored for its ability to tolerate variable climate conditions, especially its ability to persist under greatly reduced irrigation during droughts and its ability to recover production quickly after full irrigation is resumed, acting as a “shock absorber” for agricultural production under unpredictable drought conditions. The plant is also valued for fixing nitrogen in soils, reducing fertilizer costs. Perhaps most importantly, labor costs are comparatively low because alfalfa is mechanically harvested. Alfalfa is increasing in demand and price as a feed crop in the growing dairy industry of the region 21 . Any efforts to reduce water consumed by alfalfa—either through shifting to alternative lower-water crops or through compensated fallowing 20 —will need to compete with these attributes.

This new accounting provides a more comprehensive and complete understanding of how the Colorado River Basin’s water is consumed. During our study period of 2000–2019, an estimated average of 23.7 billion cubic meters (19.3 million acre-feet) of water was consumed each year before reaching its now-dry delta in Mexico. Schmidt et al. 2 have estimated that a reduction in consumptive use in the Upper and Lower Basins of 3–4 billion cubic meters (2.4–3.2 million acre-feet) per year—equivalent to 22–29% of direct use in those basins—will be necessary to stabilize reservoir levels, and an additional reduction of 1–3 billion cubic meters (~811,000–2.4 million acre-feet) per year will likely be needed by 2050 as climate warming continues to reduce runoff in the Colorado River Basin.

We hope that this new accounting will add clarity and a useful informational foundation to the public dialog and political negotiations over Colorado River Basin water allocations and cutbacks that are presently underway 2 . Because a persistent drought and intensifying aridification in the region has placed both people and river ecosystems in danger of water shortages in recent decades, knowledge of where the water goes will be essential in the design of policies for bringing the basin into a sustainable water supply-demand balance.

The data sources and analytical approaches used in this study are summarized below. Unless otherwise noted, all data were assembled for each year from 2000–2019 and then averaged. We acknowledge some inconsistency in the manner in which water consumption is measured or estimated across the various data sources and sectors used in this study, as discussed below, and each of these different approaches entail some degree of inaccuracy or uncertainty. We also note that technical measurement or estimation approaches change over time, and new approaches can yield differing results. For instance, the Upper Colorado River Commission is exploring new approaches for estimating crop evapotranspiration in the Upper Basin 22 . When new estimates become available we will update our water budget accordingly.

MCI and agricultural water consumption

The primary source of data on aggregate MCI (municipal, commercial, and industrial) and agricultural water consumption from the Upper and Lower Basins was the US Bureau of Reclamation. Water consumed from the Upper Basin is published in Reclamation’s five-year reports entitled “Colorado River—Upper Basin Consumptive Uses and Losses.” 23 These annual data have been compiled into a single spreadsheet used for this study 24 . Because measurements of agricultural diversions and return flows in the Upper Basin are not sufficiently complete to allow direct calculation of consumptive use, theoretical and indirect methods are used as described in the Consumptive Uses and Losses reports 25 . Reclamation performs these estimates for Colorado, Wyoming, and Utah, but the State of New Mexico provides its own estimates that are collaboratively reviewed with Reclamation staff. The consumptive use of water in thermoelectric power generation in the Upper Basin is provided to Reclamation by the power companies managing each generation facility. Reclamation derives estimates of consumptive use for municipal and industrial purposes from the US Geological Survey’s reporting series (published every 5 years) titled “Estimated Use of Water in the United States” at an 8-digit watershed scale 26 .

Use of shallow alluvial groundwater is included in the water accounting compiled by Reclamation but use of deeper groundwater sources—such as in Mexico and the Gila River Basin—is explicitly excluded in their accounting, and in ours. Reclamation staff involved with water accounting for the Upper and Lower Basins assume that groundwater use counted in their data reports is sourced from aquifers that are hydraulically connected to rivers and streams in the CRB (James Prairie, US Bureau of Reclamation, personal communication, 2023); because of this high connectivity, much of the groundwater being consumed is likely being sourced from river capture as discussed in Jasechko et al. 27 and Wiele et al. 28 and is soon recharged during higher river flows.

Water consumed from the Lower Basin (excluding water supplied by the Gila River Basin) is published in Reclamation’s annual reports entitled “Colorado River Accounting and Water Use Report: Arizona, California, and Nevada.” 3 These consumptive use data are based on measured deliveries and return flows for each individual water user. These data are either measured by Reclamation or provided to the agency by individual water users, tribes, states, and federal agencies 29 . When not explicitly stated in Reclamation reports, attribution of water volumes to MCI or agricultural uses was based on information obtained from each water user’s website, information provided directly by the water user, or information on export water use provided in Siddik et al. 30 . Water use by entities using less than 1.23 million cubic meters (1000 acre-feet) per year on average was allocated to MCI and agricultural uses according to the overall MCI-agricultural percentages calculated within each sub-basin indicated in Tables  1 and 2 for users of greater than 1.23 million cubic meters/year.

Disaggregation of water consumption by sector was particularly important and challenging for the Central Arizona Project given that this canal accounts for 21% of all direct water consumption in the Lower Basin. Reclamation accounts for the volumes of annual diversions into the Central Arizona Project canal but the structure serves 1071 water delivery subcontracts. We classified every unique Central Arizona Project subcontract delivery between 2000–2019 by its final water use to derive an estimated split between agricultural and MCI uses. Central Arizona Project subcontract delivery data were obtained from the current and archived versions of the project’s website summaries in addition to being directly obtained from the agency through a public information request. Subcontract deliveries were classified based on the final end use, including long-term and temporary leases of project water. This accounting also includes the storage of water in groundwater basins for later MCI or agricultural use. Additionally, water allocated to Native American agricultural uses that was subsequently leased to cities was classified as an MCI use.

Data for the Gila River basin was obtained from two sources. The Arizona Department of Water Resources has published data for surface water use in five “Active Management Areas” (AMAs) located in the Gila River basin: Prescott AMA, Phoenix AMA, Pinal AMA, Tucson AMA, and Santa Cruz AMA 31 . The water-use data for these AMAs is compiled from annual reports submitted by each water user (contractor) and then reviewed by the Arizona Department of Water Resources. The AMA water-use data are categorized by purpose of use, facilitating our separation into MCI and agricultural uses. These data are additionally categorized by water source; only surface water sourced from the Gila River hydrologic system was counted (deep groundwater use was not). The AMA data were supplemented with data for the upper Gila River basin provided by the University of Arizona 32 . We have assumed that all water supplied by the Gila River Basin is fully consumed, as the river is almost always completely dry in its lower reaches (less than 1% flows out of the basin into the Colorado River, on average 33 ).

Data for Mexico were obtained from Hernandez-Cruz et al. 10 based on estimates for 2008–2015. Agricultural demands were estimated from annual reports of irrigated area and water use published by the Ministry of Agriculture and the evapotranspiration estimates of the principal crops published by the National Institute for Forestry, Animal Husbandry, and Agricultural Research of Mexico 10 . The average annual volume of Colorado River water consumption in Mexico estimated by these researchers is within 1% of the cross-border delivery volume estimated by the Bureau of Reclamation for 2000–2019 in its Colorado River Accounting and Water Use Reports 3 .

Exported water consumption

Annual average inter-basin transfer volumes for each of 46 canals and pipelines exporting water outside of the Upper Basin were obtained from Reclamation’s Consumptive Uses and Losses spreadsheet 34 . Data for the Colorado River Aqueduct in the Lower Basin were obtained from Siddik et al. 30 Data for exported water in Mexico was available from Hernandez-Cruz et al. 10 . We assigned any seepage or evaporation losses from inter-basin transfers to their proportional end uses. All uses of exported water are considered to be consumptive uses with respect to the Colorado River, because none of the water exported out of the basin is returned to the Colorado River Basin.

We relied on data from Siddik et al. (2023) to identify whether the water exported out of the Colorado River Basin was for only MCI or agricultural use. When more than one water use purpose was identified, as well as for all major inter-basin transfers, we used government and inter-basin transfer project websites or information obtained directly from the project operator or water manager to determine the volume of water transferred and the end uses. Major recipients of exported water include the Coachella Valley Water District (California); Metropolitan Water District of Southern California (particularly for San Diego County, California); Northern Colorado Water Conservancy District; City of Denver (Colorado); the Central Utah Project; City of Albuquerque (New Mexico); and the Middle Rio Grande Conservancy District (New Mexico). We did not pursue sectoral water-use information for 17 of the 46 Upper Basin inter-basin transfers due to their relatively low volumes of water transferred by each system (<247,000 cubic meters or 2000 acre-feet), and instead assigned the average MCI or agricultural percentage (72% MCI, 28% agricultural) from all other inter-basin transfers in the Upper Basin. The export volume of these 17 inter-basin transfers sums to 9.76 million cubic meters (7910 acre-feet) per year, equivalent to 1% of the total volume exported from the Upper Basin.

Reservoir evaporation

Evaporation estimates for the Upper Basin and Lower Basin are based upon Reclamation’s HydroData repository 35 . Reclamation’s evaporation estimates are based on the standardized Penman-Monteith equation as described in the “Lower Colorado River Annual Summaries of Evapotranspiration and Evaporation” reports 17 . The Penman-Monteith estimates are based on pan evaporation measurements. Evaporation estimates for the Salt River Project reservoirs in the Gila River basin were provided by the Salt River Project in Arizona (Charlie Ester, personal communication, 2023).

Another consideration with reservoirs is the volume of water that seeps into the banks or sediments surrounding the reservoir when reservoir levels are high, but then drains back into the reservoir as water levels decline 36 . This has the effect of either exacerbating reservoir losses (consumptive use) or offsetting evaporation when bank seepage flows back into a reservoir. The flow of water into and out of reservoir banks is non-trivial; during 1999–2008, an estimated 247 million cubic meters (200,000 acre-feet) of water drained from the canyon walls surrounding Lake Powell into the reservoir each year, providing additional water supply 36 . However, the annual rate of alternating gains or losses has not been sufficiently measured at any of the basin’s reservoirs and therefore is not included in Tables  1 and 2 .

Riparian and wetland vegetation evapotranspiration

We exported the total annual evapotranspiration depth at a 30 meter resolution from OpenET 37 using Google Earth Engine from 2016 to 2019 to align with OpenET’s data availability starting in 2016. Total annual precipitation depths, sourced from gridMET 38 , were resampled to align with the evapotranspiration raster resolution. Subsequently, a conservative estimate of the annual water depth utilized by riparian vegetation from the river was derived by subtracting the annual precipitation raster from the evapotranspiration raster for each year. Positive differentials, indicative of river-derived evapotranspiration, were then multiplied by the riparian vegetation area as identified in the CO-RIP 16 dataset to estimate the total annual volumetric water consumption by riparian vegetation across the Upper, Lower, and Gila River Basins. The annual volumetric water consumption calculated over four years were finally averaged to get riparian vegetation evapotranspiration in the three basins. Because the entire flow of the Colorado River is diverted into the Canal Alimentador Central near the international border, very little riparian evapotranspiration occurs along the river south of the international border in the Mexico basin.

In addition to water consumed by riparian evapotranspiration within the Lower Basin, the Salton Sea receives agricultural drain water from both the Imperial Irrigation District and the Coachella Valley Irrigation District, stormwater drainage from the Coachella Valley, and inflows from the New and Alamo Rivers 39 . Combined inflows to the Sea during 2015–2019 were added to our estimates of riparian/wetland evapotranspiration in the Lower Basin.

Similarly, Mexico receives drainage water from the Wellton–Mohawk bypass drain originating in southern Arizona that empties into the Cienega de Santa Clara (a wetland); this drainage water is included as riparian/wetland evapotranspiration in the Mexico basin.

Crop-specific water consumption

The volumes of total agricultural consumption reported for each sub-basin in Tables  1 and 2 were obtained from the same data sources described above for MCI consumption and exported water. The portion (%) of those agricultural consumption volumes going to each individual crop was then allocated according to percentage estimates of each crop’s water consumption in each accounting unit using methods described in Richter et al. 20 and detailed here.

Monthly crop water requirements during 1981–2019 for 13 individual crops, representing 68.8% of total irrigated area in the US in 2019, were estimated using the AquaCrop-OS model (Table SI- 3 ) 40 . For 17 additional crops representing about 25.4% of the total irrigated area, we used a simple crop growth model following Marston et al. 41 as crop parameters needed to run AquaCrop-OS were not available. A list of the crops included in this study is shown in Table SI- 3 . The crop water requirements used in Richter et al. 11 were based on a simplistic crop growth model, often using seasonal crop coefficients whereas we use AquaCrop-OS 40 , a robust crop growth model, to produce more realistic crop growth and crop water estimates for major crops. AquaCrop-OS is an open-source version of the AquaCrop model 42 , a crop growth model capable of simulating herbaceous crops. Additionally, we leverage detailed local data unique to the US, including planting dates and subcounty irrigated crop areas, to produce estimates at a finer spatial resolution than the previous study. We obtained crop-specific planting dates from USDA 43 progress data at the state level. For crops that did not have USDA crop progress data, we used data from FAO 44 and CUP+ model 45 for planting dates. We used climate data (precipitation, minimum and maximum air temperature, reference ET) from gridMET 38 , soil texture data from ISRIC 46 database and crop parameters from AquaCrop-OS to run the model. The modeled crop water requirement was partitioned into blue and green components following the framework from Hoekestra et al. 47 , assuming that blue and green water consumed on a given day is proportional to the amount of green and blue water soil moisture available on that day. When applying a simple crop growth model, daily gridded (2.5 arc minutes) crop-specific evapotranspiration (ETc) was computed by taking the product of reference evapotranspiration (ETo) and crop coefficient (Kc), where ETo was obtained from gridMET. Crop coefficients were calculated using planting dates and crop coefficient curves from FAO and CUP+ model. Kc was set to zero outside of the growing season. We partitioned the daily ETc into blue and green components by following the methods from ref. 41 It is assumed that the crop water demands are met by irrigation whenever it exceeds effective precipitation (the latter calculated using the USDA Soil Conservation Service method (USDA, 1968 48 ). We obtained county level harvested area from USDA 43 and disaggregated to sub-county level using Cropland Data Layer (CDL) 49 and Landsat-based National Irrigation Dataset (LANID) 50 . The CDL is an annual raster layer that provides crop-specific land cover data, while the LANID provides irrigation status information. The CDL and LANID raster were multiplied and aggregated to 2.5 arc minutes to match the AquaCrop-OS output. We produced a gridded crop area map by using this resulting product as weights to disaggregate county level area. CDL is unavailable before 2008. Therefore, we used land use data from ref. 51 in combination with average CDL map and county level harvested area to produce gridded crop harvested area. We computed volumetric water consumption by multiplying the crop water requirement depth by the corresponding crop harvested area.

Data availability

All data compiled and analyzed in this study are publicly available as cited and linked in our Methods section. Our compilation of these data is also available from Hydroshare at: http://www.hydroshare.org/resource/2098ae29ae704d9aacfd08e030690392 .

Code availability

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Acknowledgements

This paper is dedicated to our colleague Jack Schmidt in recognition of his retirement and enormous contributions to the science and management of the Colorado River. The authors thank James Prairie of the US Bureau of Reclamation, Luke Shawcross of the Northern Colorado Water Conservancy District, Charlie Ester of the Salt River Project, and Brian Woodward of the University of California Cooperative Extension for their assistance in accessing data used in this study. The authors also thank Rhett Larson at the Sandra Day O’Connor School of Law at Arizona State University for their review of Arizona water budget data, and the Central Arizona Project for providing delivery data by each subcontract. G.L., L.M., and K.F.D. acknowledge support by the United States Department of Agriculture National Institute of Food and Agriculture grant 2022-67019-37180. L.T.M. acknowledges the support the National Science Foundation grant CBET-2144169 and the Foundation for Food and Agriculture Research Grant No. FF-NIA19-0000000084. R.R.R. acknowledges the support the National Science Foundation grant CBET-2115169.

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Contributions

B.D.R. designed the study, compiled and analyzed data, wrote the manuscript and supervised co-author contributions. G.L. compiled all crop data, estimated crop evapotranspiration, and prepared figures. S.D. compiled all riparian vegetation data and estimated riparian evapotranspiration. L.S.S. and R.R.R. accessed, compiled, and analyzed data from the Central Arizona Project. D.W. compiled data and prepared figures. A.H.-C. and S.S.-S. compiled and analyzed data for Mexico. J.C.S. compiled and analyzed reservoir evaporation data and edited the manuscript. L.M., B.L.R., and K.F.D. supervised data compilation and analysis and edited the manuscript.

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Correspondence to Brian D. Richter .

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Richter, B.D., Lamsal, G., Marston, L. et al. New water accounting reveals why the Colorado River no longer reaches the sea. Commun Earth Environ 5 , 134 (2024). https://doi.org/10.1038/s43247-024-01291-0

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DOI : https://doi.org/10.1038/s43247-024-01291-0

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