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This paper examines the security of water resources in Phoenix, AZ, under different scenarios of climate change, consumption patterns, and reductions of available surface water. Phoenix constitutes a key site for examining the projected effects of climate change on water resources in the US West. Water providers in Phoenix rely on a mix of water sources to deliver to their customers. These include groundwater, water from the Salt and Verde River watersheds, water from the Colorado River, and effluent (water reuse). Water providers in Phoenix vary in terms of their access and rights to different sources of water for municipal delivery. As a result, providers differ in terms of their exposure to cut-backs in available water. To assess vulnerability to climate change and reduced water resources available for delivery, we consider two primary questions. (1) Based on current water provider portfolio mixes, what is the current relative security of each provider's mix of water sources? (2) Using three different climate change scenarios for the Western USA and projected growth-related demand increases, what patterns of water supply vulnerabilities are likely to manifest themselves in 2030? We map projected supply shortages and discuss implications for the vulnerability of people and places and mitigation strategies.
Acknowledgements
This material is based on work supported by the National Science Foundation under Grant no. SES-0345945, Decision Center for a Desert City. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or the DCDC. We would also like to thank and anonymous Local Environment reviewer for some very helpful and constructive comments.
Notes
Portfolios refer to the particular mix of water sources individual suppliers obtain on a yearly or long-term basis. The actual content of portfolios may vary on a yearly basis depending on the availability of water from different sources for purchase by year. Some providers rely exclusively on groundwater as they lack physical access to Salt/Verde or Colorado River water.
The Upper Basin states are Colorado, Wyoming, Utah, and New Mexico; the Lower Basin states are California, Arizona, and Nevada. In addition, Mexico is by international treaty entitled to another 1.5 maf.
Both the 100-year supply figure and the 2025 safe-yield attainment date appear to be arbitrary figures selected at the time of the relevant legislation (Maguire 2007). Terms like “sustainability” or “in perpetuity” had no political purchase in these deliberations.
Critically, the Bureau of Reclamation does not use climate change models in planning for future water use and storage on the Colorado River system, choosing instead to plan based on known past flows (Powell 2008).