The University of Arizona

New Assessment Puts Southwest Climate Change Into Perspective

May 10, 2013
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Over 100 colleagues and I recently published a wide-ranging assessment of the implications of climate change for the Southwest.  The book, Assessment of Climate Change in the Southwest United States, published by Island Press, was released on May 2.  I have been thinking a lot about what we are facing in the region, and what we may face in the future.  In this blog, the first in a series based on the Assessment, I aim to distill some key results of the 500+ pages of content into just a few statements.  Future blogs, incorporating the thoughts of lead authors of specific Assessment chapters, will focus on individual issues facing our region.

Let me start with some reflection on what the book is, and what is in the book. The Assessment is not a research project, a study, or a review paper. An assessment is a critical evaluation of information for purposes of informing decisions on a complex issue: climate change and its interactions with other aspects of natural systems and society. Accordingly, the Southwest Assessment does not make policy recommendations.

The Assessment does cover climate change and variability in the six-state region from California to Colorado (CA, NV, AZ, UT, CO, NM), comprising topics ranging from the observed and projected climate of the region, to climate vulnerabilities and impacts in a variety of sectors, to considerations about the ability of the region to address climate change challenges, strategies and actions that are being taken, and observations about actions that we can choose to take. Our authors—who all volunteered their time and effort—also look at research gaps associated with scientific understanding of climate-related issues and approaches to address uncertainties.

Each of the 20 Assessment chapters was organized around a few key messages designed to highlight important findings that can be referenced by decision makers, fellow researchers, and others. Here are some examples that demonstrate the breadth of the report:

  1. Climate. The Southwest is getting hotter, with fewer cold waves and more heat waves. Southwest heat waves are projected to become longer and hotter, affecting city residents, transportation and energy infrastructure.
  2. Water. Snowmelt is occurring earlier in the year. The resulting earlier arrival of streamflow in many Southwest streams decreases water supply reliability and lengthens wildfire seasons. Climate models project continued Southwest spring season snowpack reduction.
  3. Ecosystems. Increased wildfires, outbreaks of forest pests and diseases, and forest mortality are all directly associated with higher temperatures and decreases in precipitation.
  4. Agriculture. Costly relocation of crops, irrigation conveyance systems, processing facilities, and agricultural transportation networks may be needed for tree crops—particularly if climate changes occur rapidly.
  5. Coasts. Rising sea level, high tides, storm events, and continued coastal development will increase the severity of coastal erosion, flooding, and inundation. Climate change will increase risks to coastal highways, railroads, power plants, and wastewater treatment plants.
  6. Energy. Projected increases in extreme heat waves and droughts increase the risk of electricity delivery disruption through reduced thermal power plant efficiencies, reduced transformer capacities, and the threat of wildfire to transmission infrastructure.
  7. Cities. Impermeable surfaces—like asphalt—increase temperatures, amplify heat waves, and reduce stormwater absorption, contributing to flooding and placing urban residents at risk. Major municipal utilities are studying climate influences on water supply, demand, and infrastructure.
  8. Human Health. Disadvantaged populations, including the elderly, infirm, and other persons with limited resources or access to medical care, will be more severely impacted by the increased heat waves, wildfire smoke, air pollution, and mosquito-borne diseases.
  9. Border and Tribes. The populations of the U.S.-Mexico border region and many Native Nations are more vulnerable to climate disruptions, due to unresolved water rights, a history of socio-economic and political marginalization, and cultural differences.

Ever since I saw Phil van Mantgem show a version of the graph to the right at the 2012 Mountain Climate Research Symposium (MtnClim 2012), I have been incorporating it into my talks on the findings of the Assessment. Climate, and therefore climate change, is pervasive in space (across the vast landscapes) and in time—from its influence on daily extreme heat or extreme storm events to the cumulative effects of seasonal, annual, or multidecadal episodes of drought.  Because climate is pervasive, influencing everything from water (“Climate change is water change,” says Assessment co-author Brad Udall), to air quality, to coastal erosion, the chances are very good that multiple aspects of society and the environment will be affected simultaneously, as frequently occurs during a slow-onset disaster like drought. So, this humorous illustration provides an analogy to an obvious but important point about the effects of climate change: they will affect us the most when they intersect.

Intersecting and cascading effects burden our infrastructure, economy, and human resources, increasing the time required for systems to recover. While we will still experience a fire in one place this year and a flood next year in another place, we will increasingly experience interconnected impacts—to water supplies, forests, wildfire occurrence, wildlife habitat, floods, public health, and more. A simple but poignant example is from New Mexico in the summer of 2011.  The late spring Las Conchas fire, which decimated forests in an area whose economy depends a great deal on tourism and recreation, also triggered water woes when summer monsoon rains washed ash and sediment downstream, clogging Cochiti Reservoir, a main drinking water supply for Albuquerque. Water quality and water withdrawals were affected for months; the impacts demonstrated that upstream forests and downstream cities really are joined at the hip. Climate change projections for hotter and drier conditions in parts of the Southwest, accompanied by increased evaporation, forest stress, and possibly more extreme precipitation, make this kind of scenario more likely in the future.

With these intersecting and interconnected impacts of climate change, am I suggesting climate change gloom and doom like in the movie, “The Day After Tomorrow?”  No, I believe that we are up to the task of preparing for and managing the effects of climate change, and my colleagues point out that historically, the people of the Southwest have shown great capacity to respond to environmental stress and to steward our natural resources. They spotlight many regional revenue-generating opportunities for reducing heat-trapping emissions through energy efficiency and the development of renewable energy, and many options for dealing with climate change challenges to water and ecosystem resources (see Assessment Chapter 18, Climate Choices for a Sustainable Southwest). But it will not be a cake walk either.

So, if I were to have the ear of a policymaker in the region, I would recommend integrated climate change planning that acknowledges the connections between climate, environment, resource management sectors, economic activities, infrastructure, public health and safety, and predisposing factors such as changes in population growth and socio-economic status. This is similar to the approach taken by the Bureau of Reclamation's thoughtful multi-year Colorado River Basin Water Supply and Demand Study, where participation by all potential stakeholders was invited and multiple future scenarios, encompassing many different resource needs and options, were developed.  Addressing concerns individually and ignoring how the actions taken to manage one resource or public service affect other resources, economic activities, or services is no longer an option.

To highlight some of the other important Assessment insights, we’ll be posting more blogs here in the coming weeks based on interviews of various authors about key insights in different chapters. Stay tuned!

*For more information on the Assessment, including 2-page fact sheets of each chapter and to download a pdf of the book, visit