We developed a provider-based water management and planning model for the Phoenix Metropolitan Area of Central Arizona.  Adapted from WaterSim 2.0, the model combines a systems dynamics model (PowerSim),Microsoft C-Sharp, and the PowerSim® Studio Software Development Kit (SDK) to simulate the spatial and temporal dynamics of current and projected water supply and demand as influenced by population demographics, climatic uncertainty, and ground water availability.  Central to this structure was the ability to examine current and potential vulnerability in a water provider's portfolio.  The portfolio describes whether water supplies come from surface water sources, groundwater pumping, or both.  Water demand was estimated from residential density, population projections, water duty, and acreage within the provider service area.  Initial estimates of groundwater for each provider were simulated using the Arizona Department of Water Resources Salt River Valley (SRV8306) groundwater model.  We propose that providers have differing vulnerabilities to climate, groundwater reserves, or both depending on their portfolio.  To test this we examined potential vulnerability for each provider by simulating their reliance on groundwater for 2009 to 2034 using the Maricopa Association of Governments population projections and reductions in runoff that amounted to 90% to 50% of the historical estimate, in 10% intervals.

Results/Conclusions

Vulnerability to climate increased with increased projected population (above 200%) in association with decreased initial groundwater and a low groundwater designation.  Providers with low reliance on groundwater had, in general, low growth projections (these providers have a long settlement history). Groundwater vulnerability was greatest for providers that rely solely or heavily on groundwater in conjunction with high, or moderately high groundwater designations. These providers have, in general, low groundwater reserves and high population growth estimates due to a short settlement history. A few of providers withdrew up to 400 million m³ of water over the 25-year period. Simulations suggest that mining groundwater at this rate is not sustainable and will result in insufficient groundwater to meet the projected growth estimates for these providers. On-going model development will incorporate provider-based policy options that will enable “what-if” scenarios to examine policy trade-offs and their effect on water availability, consumption, and sustainability as influenced by climatic uncertainty and changing populations for Valley water providers.