2025 Orange County Water Demand Projection Model
1. Introduction The Municipal Water District of Orange County (MWDOC) supplies water to 26 retail agencies and the Orange County Water District (OCWD). The 3 cities: Anaheim, Fullerton, and Santa Ana, who are direct customers of the Metropolitan Water District of Southern California (MWD) are also analyzed to provide a complete picture of the county. Water demand forecasts are a foundational element of water supply and infrastructure planning. MWDOC, OCWD, and representatives of the retail agencies selected an econometric model approach for the update. Hazen and Sawyer (Hazen) developed the demand model was developed by regressing historical water consumption against several explanatory variables known to influence water demand (including weather, water price, regional economic conditions, and housing density). This technical memorandum (TM) describes the econometric demand model developed to produce regionally consistent forecasts across all Orange County agencies. Model development was funded by both MWDOC as the imported water wholesale provider and OCWD the OC Groundwater Basin manager. Table 1-1 highlights a range of available approaches to long-term demand forecasting. Among these, an econometric approach incorporates high-resolution data at the agency scale and integrates many explanatory variables to properly identify the individual influence of each variable on historical and future demand.
Table 1-1: Pros and Cons of Several Demand Models
Model
Pro’s
Con’s
Trends are simply extended into the future Model provides no indication of what causes trends in water use GPCD is often held constant at the historical rate No indication of what causes trends in GPCD Consists of many assumptions for each time period Difficult to explain observed variability in water use due to weather, price, or demographic influences Difficult to address the historical impacts of technology Statistical parameters contain a degree of potential error Uncertainty in future values of inputs
Simple and easily estimated in a Spreadsheet
Time Series
Ability to decouple the rate of water use from growth
Gross per Capita
Estimates the amount of use associated with individual purposes Addresses technological change and water use efficiency Links water use statistically to explanatory variables Provides estimates of how variability in explanatory factors affect water use Allows for scenario design around inputs
End Use Accounting
Regression (Econometric)
1-1
Appendix G - 17
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