National Climate Assessment Foresees Alarming Impacts on Southwest

Back to Winter 2013 Newsletter

By Katharine Mitchell, WRRC Graduate Outreach Assistant

The Southwest is considered one of the most ‘climate-challenged’ regions of North America. The overwhelming heat of summer seems distant to many desert dwellers in Arizona. Residents cannot ignore the great fluctuation in temperatures this season. Scientists are bringing to the public’s attention the fact that changes are affecting Arizona’s climate, and that human activities are the driving force. Projected regional temperature increases, amplified by the way that our growing cities retain heat, will pose increased threats to public health. Rising temperatures and drought conditions will foster more severe wildfires. Snowpack and stream flow amounts are projected to decline, decreasing water supply for cities, agriculture, and ecosystems. These key findings on the changing climate’s effects on the Southwest have been detailed in the recent draft of the National Climate Assessment. The draft of the Third National Climate Assessment Report was approved by the sixty-person National Climate Assessment Development and Advisory Committee (NCADAC) and released for public comment.  This draft assessment arrived days after the National Oceanic and Atmospheric Administration (NOAA) issued its annual State of the Climate report, noting that 2012 was the hottest year on record.

The Southwest is one of eight regions assessed in the report, with a chapter dedicated to the most recent science on climate change impacts for Arizona, California, Colorado, Nevada, New Mexico, and Utah. A central component of the assessment process was the Southwest Regional Climate assessment workshop that was held on August 1-4, 2011 in Denver, CO. With more than eighty participants, a series of scoping presentations and workshops began the process leading to a foundational report. Uncertainties still remain pertaining to projection of regional climate and hydrology.

Competition over scare water resources in the Southwest will only intensify over the coming years. Compared to temperature, precipitation levels vary considerably across the Southwest with portions experiencing both increases and decreases. Arizona is predicted to experience significant decreases in precipitation levels, with some uncertainty in the southern areas of the state. The authors state with certainty that there will be a continued decrease in snowpack and stream flows. Rising temperatures and drought have caused earlier spring snowmelt, and shifted runoff to earlier in the year. Precipitation extremes in winter will become more frequent and more intense (i.e. more precipitation per hour). Large portions of the Southwest will experience reductions in runoff, stream flow, and soil moisture in the mid-to late-twenty first century. In some areas, surface water quality will be affected by the scarcity of water, higher rates of evaporation, higher runoff due to increased precipitation intensity, flooding, and wildfire. Discussions will need to continue to address demand pressures, and the shared vulnerabilities of ground water and surface water systems.

Both urban and rural populations in Southwestern cities are highly dependent on the supply of drinking water, and irrigation water for agricultural use. The projected decline in snowpack and stream flow will lead to the decrease in recharge and water supply for human and ecological consumption. The report presents evidence of irrigation dependence, and the vulnerability of high value specialty crops to extremes of moisture, cold, and heat. The report points to potential critical changes in key sectors, such as agriculture, energy production, and public health. As high temperatures and more persistent droughts affect southern Arizona, in particular, this will cause a shift in agriculture north, which also poses an economic concern over the loss of jobs.

Excessive wildfires are a concern as they destroy homes, expose slopes to erosion and landslides, threaten public health and safety, and lead to economic losses. Wildfire and bark beetles killed trees across twenty percent of Arizona and New Mexico forests from 1984 to 2008. The conifer forests of Arizona’s sky islands are notably threatened. Prescribed burning, mechanical thinning, and retention of large trees can help forest ecosystems adapt to climate change.

The delivery of electricity may become more vulnerable to disruption due to extreme heat and drought events. The threat of rising temperatures, and the effects of the “urban heat island”, will make the region’s cities uncomfortable places to live.  Rapid population growth is particularly a challenge in this region where ninety percent of the population lives in cities.  The most vulnerable populations, such as the elderly, will be most at risk. The increased chance of power outages poses a serious threat to safety and mortality. Heat stress has been found to be a recurrent health problem for urban residents, and the highest rates of heat-related deaths have been found in Arizona, notably Phoenix.

The National Climate Assessment has set out to serve as a comprehensive and inclusive overview of the science of climate change and its effects on communities in regions across the country. “If it survives in substantially its current form, the document will be a stark warning to the American people about what has already happened and what is coming,” New York Times reporter, Justin Gillis wrote. The stakeholder participation and communication strategy for the report sets it apart from previous U.S. climate assessments.  Efforts to educate will be ongoing and reports will be a continuing effort rather than a periodic report-writing activity.  The process will include an evaluation of the Nation’s progress in adaptation and mitigation and involve long-term partnerships with non-governmental entities.  The continuing process also will build capacity for assessments in regions and sectors.  The assessment includes new methods for documenting climate related risks and opportunities and provide web-based information that supports decision making processes within and among regions and sectors of the U.S.

The assessment will contribute directly to the U.S. climate policy debate, informing the public and key decision makers on how to adapt to a changing climate. Gregg Garfin, of the University of Arizona, Institute of the Environment and the School of Natural Resources and the Environment, led the production of the Southwest Regional chapter along with Guido Franco of the California Energy Commission. Andrew Comrie, University of Arizona Professor in the School of Geography and Development, was among the group of six lead authors for the Southwest chapter, representing the University of Southern California, University of Nevada (Las Vegas), Colorado State University, National Park Service, and NOAA. The authors engaged local stakeholders through regional town hall meetings, to bring together climate change experts and users of climate change information, from academia; local, state, tribal, and federal governments; non-profit organizations; and business and industry.

More than 240 authors have been engaged since the start of this effort. The Global Change Research Act of 1990 mandates that a national climate assessment be conducted every four years. The last assessment was published in 2009, with this newly released draft of the Third National Climate Assessment to result in a final report due in second half of 2013. Early in the two-year process, the National Climate Assessment identified stakeholders through a model for organizing and thinking about individuals and groups that may be engaged at various points in the process. Established under the Department of Commerce in December 2010, and supported through NOAA, the sixty-person National Climate Assessment Development and Advisory Committee were assembled to act as a consultative body for the National Climate Assessment.  Committee members are diverse in background, expertise, geography, and sector of employment. The draft report is available to download online, and the comment period is open from January 14 – April 12, 2013. During the open public comment period, the report will also be under review by the National Research Council. The authors will use the comments received to revise the report before submitting the final draft to the government for consideration.

Arizona’s future under the influence of climate change will be significantly warmer and drier than in the past, and the impacts will affect the regions’ water, forests, wildfires, ecosystems and ability to grow crops. The effects of climate change are already visible across the region. The draft report paints a sobering picture of existing conditions and of the climate future we face if action is not taken by decision makers, and the public at large. The authors state that "Climate change, once considered an issue for a distant future, has moved firmly into the present.”