Phoenix, Portland study brings policy into focus

Phoenix and Portland: It is hard to imagine two more mismatched American cities in terms of climatic conditions, economies, public attitudes and growth-management policies.

When it comes to answering important scientific questions, however, differences can be a plus, inviting comparisons and bringing commonalities into sharper relief.  

Such is the idea behind the latest project of ASU’s Decision Center for a Desert City (DCDC), a comparative study of the relationship between land use, climatic conditions and water demand. Portland State University and Clark University in Worcester, Mass., will join DCDC in the research, which has received almost $300,000 from the Sectoral Applications Research Program (SARP), part of the National Oceanic and Atmospheric Administration (NOAA) Climate Program.

The research will examine how land use planning and water resource management are, or might be, integrated to address water stress in two metropolitan regions with different patterns of exposure and adaptation to climate changes.

“Comparative regional studies help us determine the extent to which water demand is influenced by climatic conditions and land-use patterns across neighborhoods and cities with varying environmental and social characteristics,” says Kelli Larson, the co-principal investigator on the project and assistant professor in the School of Geographical Sciences and Urban Planning and the School of Sustainability.

Phoenix, a sprawling desert city with a population expected to double over the next 40 years, depends upon water from the Salt, Verde and Colorado Rivers, transported via canals to the city, along with groundwater. Portland, a growth-controlled river city with approximately half the population of metro Phoenix and approximately 5 times its average annual rainfall (42.7 inches versus 8.3 inches), depends upon winter rains and storage in the reservoirs of the Bull Run Watershed.

One vital commonality, driving and informing the project, links the two cities, and that is that they are located in the West, where recent research suggests climate change may inflict significant changes in the coming years, according to Patricia Gober, the co-director of DCDC and co-principal investigator on the project with Larson.

“Phoenix and Portland share something important in common with one another and with numerous other metropolitan areas globally,” Gober says. “They are increasingly vulnerable to water shortages from climate variability, climate change and rapid population growth.”
Phoenix and Portland already are experiencing climatic deviations with the Pacific Northwest seeing more frequent winter floods and summer warming while the Southwest languishes in the midst of a multiyear drought.

The future could present additional challenges. A 2007 report by the National Research Council suggests a warmer and drier future for the Southwest, one with  reduced snowpack, Colorado River flows and water availability to Phoenix.

As for Portland, long-term climate models suggest higher temperatures are likely in the Pacific Northwest. This, combined with increased precipitation, could lead to rising snow elevations that would affect the timing of snowmelt and summer stream flow, ultimately affecting the timing of water resources in the city of Portland surface supply system.

Heejun Chang, an associate professor of geography at Portland State University and the principal investigator of the new NOAA grant, says that the amplification of Portland’s seasonal cycle could lead to problems.

“As we get hotter summers, water demand is likely to increase, so some small water providers are increasingly concerned about potential water stress in their service areas,” Chang says.

According to Chang, the greater concern for Portland water managers is seasonal water shortage resulting from population growth rather than climate change, although they acknowledge that they would like to plan for changing climate.

“This is particularly the case for municipalities that rely on reservoirs primarily fed by rainwater,” he says.

The researchers will downscale water and energy flux models to the neighborhood level and investigate interrelationships among land cover, temperature change and water consumption. Then they will combine the results of the analysis with various downscaled global climate change scenarios to simulate the effects of long-term climate change on water demand.

The project also aims to identify hotspots of potential water-resource vulnerability or resilience under different combinations of urban growth and climate change and consult closely with regional water providers and land-use planners to make sure the results are as usable and relevant as possible for decision-making.

Nick Gerbis, nicholas.gerbis@asu.edu
Decision Center for a Desert City