About Report

Assessment of Climate Change in the Southwest United States—a contribution to the 2013 National Climate Assessment—is a summary and synthesis of the past, present, and projected future of the region’s climate, emphasizing new information and understandings since publication of the previous national assessment in 2009.

Regional scope

  • The assessment examines what climate and climate change mean for the health and well-being of human populations and the environment throughout the Southwestern United States, an area of about 700,000 square miles.
  • The region includes Arizona, California, Colorado, Nevada, New Mexico, and Utah, vast stretches of coastline, an international border, and the jurisdictions of 182 federally recognized Native American tribes.
  • With its regional perspective, this assessment also provides a foundation for assessments to be made for decision making at finer scales.

Comprehensive approach. The assessment looks at:

  • climate and its effects, on scales ranging from states to watersheds and across ecosystems and regions;
  • links between climate and resource supply and demand;
  • effects on sectors—such as water, agriculture, energy, and transportation— that are critical to the well-being of the region’s inhabitants;
  • the vulnerabilities to climate changes of all facets of the region; and
  • the responses and preparedness plans that society may choose to make.

Expert contributors

  • The assessment represents the findings of 120 authors, representing a variety of disciplines, who have discussed and made judgments about the importance, quality, and limitations of the information used in the assessment.
  • The assessment is guided, in part, by stakeholders who identified issues of concern within the region and made comments at meetings and online.
  • In addition, the assessment received two independent reviews. 

Data sources

  • The assessment evaluates and synthesizes information from a range of sources, including data sets of observations, simulations and projections from computer modeling, peer-reviewed scientific papers, case studies, and other sources.
  • This assessment is evidence-based as verified by multiple reviews. Authors have clearly labeled and consistently judged the importance of information and their level of confidence in the assessment’s key findings.
  • To ensure transparency in developing this regional assessment’s conclusions and key findings, we also have cited all sources of information, as is common peer-review practice, and sources of data for all graphics and tables.

Knowledge gaps and research needs

  • The assessment presents key uncertainties associated with the topics it discusses, and identifies important gaps in knowledge about climate change and the type of research that would reduce or better define areas of uncertainty. 


  • The assessment was supported by funding from the National Oceanic and Atmospheric Administration (NOAA) Climate Program, RISA program (through CLIMAS, CNAP and WWA), the Department of the Interior (through the Southwest Climate Adaptation Science Center), by the unpaid contributions of authors and reviewers.