Researchers Release Major Draft Assessment of Climate Change Impacts on the Southwest

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The Southwest Climate Alliance released today a review draft of the Assessment of Climate Change in the Southwest United States.  It is the first regional climate assessment of the Southwest in over a decade during which evidence of climate change and its impacts have rapidly emerged in the region.  Though not proceeding apace, actions in the region to prepare for future impacts are emerging -- even as efforts to address climate change at the Federal level have been stymied.


The Southwest region covers six states—Arizona, California, Colorado, Nevada, New Mexico, and Utah. According to the report Web site, it is "an area that includes vast stretches of coastline, an international border, and the jurisdictions of nearly two hundred Native Nations."

The report is available as separate draft chapters, with every page marked "DRAFT For Review Only" and saying: "Do not quote,cite or reproduce this document." What it does not say is READ THIS DOCUMENT!, as it certainly should be read -- particularly Chapter 1: Summary for Decision Makers (which will not be available until Friday, 30 March). 

Meanwhile, for a very brief and readable overview of impacts in the region, see the Southwest chapter of the 2009 report from the U.S. Global Change Research Program (USGCRP), Global Climate Change Impacts in the United States.

Above: Illustration from the Southwest chapter of  Global Climate Change Impacts in the United States, published in 2009.  The figure indicates that under both the low and high emissions scenarios, March-April precipitation is likely to decline by 2080-2099 relative to 1961-1979-- with the decline most severe under the high emissions scenario.  Source: USGCRP.

The new draft Southwest assessment report has been submitted to the USGCRP's National Climate Assessment (NCA), where it will be used as one basis for the NCA report currently under development. A draft of the NCA report, with a brief chapter for each region of the U.S., is supposed to be released for public review at the end of 2012. The last major regional assessment of the Southwest produced by the USGCRP was published a dozen years ago in September 2000.  Under the Global Change Research Act of 1990, an assessment is required "not less frequently than every 4 years."

The new draft Southwest assessment report was released on the same day the Intergovernmental Panel on Climate Change released its report on  Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (see International Panel Highlights “Climate Resilient Cities,” as Communities Mobilize for Changing Weather Patterns) and just three days before the City of Tucson holds its "Power to Prepare Tucson" Summit (see "Power to Prepare Tucson" Summit: Faced with more Extreme Weather Patterns, Citizens Engage in Arizona City's Climate Preparedness Efforts).

Contents of the Draft Report

The chapters of the draft Southwest assessment are as follows (descriptions provided by Southwest Climate Alliance; all links are to PDF files):

Chapter 1: Summary for Decision Makers.  The chapter highlights the key findings of the report.

Chapter 2: Overview.  This is a roadmap of the report summarizing the content of each chapter as well as the NCA guidance, our transparency in creating this report, and reviews relationship to previously written national and southwest focused assessments.

Chapter 3: The Changing Southwest. Provides background on the important characteristics that affect exposure and sensitivity of the Southwest to climate change examining general socio-economic and land use patterns and trends that are occurring in the region. These include a brief examination of the physical context, human demographics and population trends, key laws relevant to resource management, and institutions conducting climate assessment or policy initiatives.

Chapter 4: The Weather and Climate of the Southwest. Describes baseline characteristics of current climate and hydrologic parameters, such as temperature, precipitation, and snowpack, as well as the factors that contribute to the unique climates of the region. Chapter 4 discusses the main factors contributing to regional climate variability, and describes important climate hazards and impacts, such as droughts, floods, wildland fires, air quality and extreme temperatures.

Chapter 5: Evolving Weather and Climate Conditions of the Southwest. Assesses weather and climate variability and trends in the Southwest, using observed climate and paleoclimate records. Chapter 5 analyzes the last 100 years of climate variability in comparison to the last 1000 years, and links the important features of evolving climate conditions to river flow variability in four of the region’s major drainage basins. The chapter closes with an assessment of monitoring and scientific research needed to increase confidence in understanding when climate episodes, events, and phenomena are attributable to human-caused climate change. 

Chapter 6: The Southwest Climate of the Future - Projections of Mean Climate.   Presents climate model projections, for the Southwest, of future temperature, precipitation and atmospheric circulation (long-term weather patterns). Chapter 6 also examines projections of hydrologic parameters, such as snow water equivalent, soil moisture, and runoff for a subset of basins in the region, including the Colorado River Basin.

Chapter 7: The Southwest Weather and Climate Extremes of the Future. Summarizes current scientific understanding about how specific weather and climate extremes are expected to change in the Southwest, as global and regional temperatures increase (i.e., "global warming"). Chapter 7 examines heat waves, cold snaps, drought, floods, and fire weather. The chapter also examines possible changes in weather patterns associated with climate extremes, such as atmospheric rivers and Santa Ana winds.

Chapter 8: Natural Ecosystems. Addresses the observed changes in climate that are associated strongly with observed changes in geographic distributions and phenology of species in terrestrial and freshwater ecosystems. Chapter 8 examines disturbance processes such as wildfires and outbreaks of forest pathogens. The chapter also discusses issues associated with the uptake and sequestration of carbon in Southwest ecosystems, as climate changes.

Chapter 9: Coastal Issues. Examines physical threats, associated with climate change projections, to current coastal ecosystem structure, function, and management. The chapter describes and evaluates key climate-induced impacts, including sea level rise, erosion, and storm surges, and oceanographic factors, including the effects of changes to nutrient upwelling, ocean acidification, and hypoxic (oxygen depleted) zones. Chapter 9 also describes interactions between existing vulnerabilities, such as human development in coastal ecosystems, and climate change threats. The chapter concludes by examining adaptation options, including infrastructure development, planning, and insurance incentives.

Chapter 10: Water Impacts. Focuses on societal vulnerabilities and societal impacts to changes in sources, timing, quantity, and quality of the Southwest’s water supply. The chapter addresses potential changes to hydrology, floods and water quality; vulnerabilities related to environmental factors, such as fire and stream temperatures; and issues related to water management, such as water and energy demand, and reservoir operation. Chapter 10 describes water management strategies for the coming century, including federal, regional, state and municipal adaptation initiatives.

Chapter 11: Agriculture and Ranching.  Reviews the climate factors influencing crop production and agricultural water use. The chapter discusses modeling studies that use climate change model projections to examine effects on agricultural water allocation, and scenario studies that investigate economic impacts and the potential for using various adaptation strategies to accommodate changing water supplies, crop yields, and pricing. Chapter 11 concludes with sections on ranching and drought, and the use of disaster relief programs as a climate adaptation strategy.

Chapter 12: Energy Impacts. Describes the potential effects of climate change on the production, demand, and delivery of energy. Chapter 12 describes climate effects on peak energy production, and examines vulnerabilities of infrastructure to direct and indirect climate changes. The chapter delves into issues associated with multiple sources of power generation, fuel mixes for energy generation and transportation, and offers mitigation strategies for the present and future.

Chapter 13: Urban Areas.  Describes the unique characteristics of Southwest cities and the ways in which they will be affected by and contribute to future climate changes. The chapter draws particular attention to six representative large urban areas in the six Southwest states – Albuquerque, Denver, Salt Lake City, Las Vegas, Phoenix and Los Angeles. Chapter 13 addresses ways in which cities may contribute to climate change through their urban metabolisms – flows of water, energy, materials, nutrients, air, water and soil impacts. The chapter also examines key pathways through which cities will be affected, including fire, water resources, flooding, urban infrastructure, and sea level rise. The chapter concludes with a critical evaluation of data and monitoring needs to improve the basis for making adaptation decisions.

Chapter 14: Transportation.  Examines climate change issues across the broad range of transportation sectors in the Southwest – including land transportation (passenger, freight), marine transportation, and air transportation – beginning with current trends. Chapter 14 analyzes potential direct and indirect effects to infrastructure, economic, and human health. The chapter concludes by examining vulnerabilities and uncertainties with respect to potential disruptions to the transportation system.

Chapter 15: Health Effects of Climate Change in the Southwest. Reviews the state of knowledge with regard to climate-related public health threats, including those related to extreme heat, air quality (including respiratory ailments, dust, and fire-related particulate), and changes to disease vectors (such as mosquito populations). Chapter 15 examines factors that interact and complicate disease transmission and attribution of risk. The chapter concludes by discussing public health planning and factors related to adaptation planning.

Chapter 16: Impacts of Future Climate Change in the Southwest on Border Communities. Evaluates the drivers of social vulnerabilities to climate change, including border demographic changes, urban and peri-urban expansion, socioeconomic issues that are unique to the U.S.-Mexico border,and energy, transportation and water issues. Chapter 16 also addresses border climate and ecosystem issues, such as climate extremes, wildland fire, and potential climate effects on the Colorado River estuary. The chapter includes a discussion of prospects and challenges to implementation of border adaptation measures, with an emphasis on the role of cross-border collaboration.

Chapter 17: Unique Challenges Facing Southwestern Tribes: Impacts, Adaptation and Mitigation. Evaluates observed climate effects on Native American lands, and discusses the intersection of climate and the unique cultural, socioeconomic, legal and governance context in addressing these issues in Indian Country. Chapter 17 highlights the preparedness, mitigation and adaptation planning initiatives currently underway in the Southwest.

Chapter 18: Climate Choices for a Sustainable Southwest. Describes challenges to implementing mitigation and adaptation plans, given specific issues related to state, municipal, and regional institutions governance. The chapter discusses the recent of environmental management initiatives in the region, and gives numerous examples of current climate change mitigation and adaptation initiatives and successes. Chapter 18 analyzes the barriers to implementing solutions, and the practical opportunities afforded through maximizing the co-benefits of mitigation and adaptation, and minimizing costs and environmental and social harms.

Chapter 19: Moving Forward with Imperfect Information.  Builds on information from previous chapters, with regard to uncertainties, scientific, monitoring and data challenges. Chapter 19 summarizes the scope of what we do and do not know about climate in the Southwestern United States, and outlines those uncertainties that hamper scientific understanding of the climate system and potentially impede successful adaptation to the impacts of climate change. The chapter emphasizes issues related to climate and impact models, and scenarios of the future.

Chapter 20: Research Strategies for Addressing Uncertainties. Builds on descriptions of research and needs articulated in earlier chapters in the report. The chapter explores strategies to improve characterization of changes in climate and hydrology, and emphasizes the application of research strategies to decisions, including methods such as scenario planning. The chapter describes current research efforts and the challenges and opportunities for reducing uncertainties.

The Southwest Climate Alliance and the Assessment Review Process

The Southwest Climate Alliance (SWCA) is a consortium of research institutions in the Southwest, including National Oceanic and Atmospheric Administration's (NOAA) Regional Integrated Sciences and Assessments (The Climate Assessment for the Southwest, The California-Nevada Applications Program, and the Western Water Assessment) and the U.S. Department of Interior's Southwest Climate Science Center.

The SWCA will accept comments on the draft report through 11:59 PM (PDT) April 11, 2012.  Reviewers should register at to submit comments.

The Southwest Climate Science Center is planning a Southwest Climate Science Summit to be held in Tucson, Arizona, June 11 - 14, 2012.  See the announcement (PDF).

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