A provider-based water planning and management model--WaterSim 4.0--for the Phoenix Metropolitan Area

Area of Science:

• Environmental Modeling and Simulation
• Water Resource Management
• Urban Hydrology

Background:

• Phoenix Metropolitan Area faces significant future water demand increases, potentially eightfold by 2030.
• Uncertainty in future water supplies is a major challenge for the region.
• Existing water management models require enhancement to address complex supply and demand dynamics.

Purpose of the Study:

• To develop and describe WaterSim 4.0, a provider-based water management and planning model for Phoenix.
• To simulate the spatial and temporal dynamics of water supply and demand under various scenarios.
• To analyze the impact of population demographics, climatic uncertainty, and groundwater availability on water resources.

Main Methods:

• Developed WaterSim 4.0, integrating a FORTRAN library with Microsoft C# for simulation.
• Estimated water demand using residential density, population projections, water duties, acreage, and per capita consumption.
• Incorporated groundwater availability from the Arizona Department of Water Resources (ADWR) Salt River Valley groundwater flow model (GFM).
• Conducted sensitivity analysis by modifying runoff (80%-110% of historical estimates) for 33 providers over 25 years.
• Assessed provider responses using groundwater reliance (GWR) and cumulative groundwater withdrawals.

Main Results:

• Identified four distinct groups of water providers based on their water portfolio and response to altered surface water availability.
• Water portfolios heavily reliant on Colorado River water showed higher sensitivity to potential surface water supply reductions.
• Greatest groundwater depletions were observed in communities entirely or nearly entirely dependent on groundwater with high demand projections.

Conclusions:

• WaterSim 4.0 provides a robust framework for analyzing water management strategies in Phoenix.
• Provider-specific vulnerabilities to water supply fluctuations and groundwater depletions were quantified.
• Ongoing model development aims to enhance groundwater modeling precision and enable policy 'what-if' scenario analysis for long-term sustainability.