Item 21 - Public Hearing - Resolutions Approving the 2025 Urban Water Management Plan and the 2025 Water Shortage Contingency Plan

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2025 URBAN WATER MANAGEMENT PLAN MAY 2026/FINAL DRAFT/CAROLLO presumed drought conditions. Together, the water service reliability assessment, DRA, and water shortage contingency planning allow Santa Ana to have a comprehensive picture of its short-term and long-term water service reliability and to identify the tools to address any perceived or actual shortage conditions. CWC Section 10612 requires the DRA to be based on the driest five-year historical sequence for Santa Ana's water supply. However, CWC Section 10635 also requires that the analysis consider plausible changes on projected supplies and demands due to climate change, anticipated regulatory changes, and other locally applicable criteria. The following sections describe the methodology and results from Santa Ana's DRA. 7.5.1 Methodology As described in more detail in Chapter 4, the water demand forecasting model prepared for Santa Ana isolated the impacts that weather and future climate can have on water demand through the use of an econometric model. In addition to weather related factors, the model incorporates explanatory variables that influence both historical and projected water use, including water price, gross domestic product, median household income, housing density, persons per household, households per account, sectoral employment mix (for commercial, industrial, and institutional demand), seasonal patterns, historical conservation trends, drought restrictions, and COVID-19 behavioral effects. These variables allow the model to separately quantify how economic conditions, demographic shifts, land use characteristics, and institutional constraints affect demand across residential, commercial, industrial, institutional, and irrigation sectors (MWDOC, 2025). The impacts of hot/dry weather conditions are reflected as a percentage increase in water demands from the average condition (average of FY 2017-18 and FY 2018-19). For a single dry-year condition (FY 2013-14), the model projects a three percent increase in demand for Santa Ana's service area (MWDOC, 2025). The model used a 33-year dataset (1991-2024) to estimate demand under average (normal), single-dry year, and five consecutive dry years hydrologic conditions. Correlation coefficients between demand, temperature, and precipitation were applied to the hottest and driest historical sequences to calculate high-demand scenarios,which were expressed as scaling factors relative to the 33-year average demand. For Santa Ana, the five consecutive dry year demand scenario is based on the demand model's multiple dry year methodology. In accordance with the econometric demand model approach used to develop UWMP demand projections, a single hot/dry year was first identified based on weather conditions that produced the greatest demand response. Consecutive dry years were then represented by applying incremental scaling factors to this single hot/dry year demand to account for the compounding effects of persistent warm and dry conditions over time.These scaling factors show long-term relationships between regional water use and multi-year temperature and precipitation deficits and are applied sequentially to simulate second through fifth consecutive dry years. This approach is consistent with the demand modeling framework summarized in Table 7.1 and 7.7. 7.5.1.1 Water Demand Characterization Beyond local groundwater supplies, Santa Ana's remaining water supplies are purchased from MET, regardless of hydrologic conditions. As described in Chapter 6, MET's supplies are from the Colorado River, SWP, and in-region storage. In MET's 2025 UWMP, the DRA concluded that even without activating CITY OF SANTA ANA