2025 Orange County Water Demand Projection Model
forecasts are reflected by projected departure values of 0 for the precipitation and temperature variables. Future weather inputs for the irrigation sector consist of monthly normal precipitation values. Alternative demand scenarios ( Section 5 ) consider the potential effects of climate change on precipitation and temperature using CMIP6 data from CalAdapt. CMIP6 represents the sixth phase of the World Climate Research Program (WCRP) Coupled Model Intercomparison Project (CMIP) and includes 134 models from 53 modelling centers. CMIP6 relies on Shared Socio-economic Pathways (SSPs) that describe plausible futures of societal development and impacts on greenhouse gas emissions. A 2021 report explains why the CalAdapt models best represent the California climate. 3
4.2.3
Water Price
Projections of future water rates were included as an explanatory variable in the water demand model. The future values for water prices assumes 5 years of a 3% (above inflation) increase in price per year, after which prices are held at nominal prices adjusted for inflation. Additional water pricing scenarios can be generated as agencies formulate and become more certain about future price paths.
4.2.4
Detrended Economic Factor
The future economy was assumed to run at its long-run trend rate of growth; thus real GDP is assumed to increase at the long-term rate. The detrended GDP value used to project future demands is 0, indicating no difference from the long-term GDP growth.
4.2.5
Median Income
Median income was included as an explanatory variable in the water demand model. Median income by retailer was held constant at the historical 2024 level, denominated in inflation-adjusted 2022-dollar values.
4.2.6
Housing Density
Housing density was included as an explanatory variable in the single-family and multifamily residential model sectors. Separate variables were created for single-family housing density and multifamily housing density. The baseline density projection assumed a “build up” scenario where housing units could vary within a constant land area, thereby affecting average density. Future values for the density variables are derived from the projected number of single-family or multifamily housing units ( Section 2 ) divided by the land area classified as residential land use within the retail service area boundary (which is assumed to stay constant throughout the forecast).
3 Interim Deliverable for EPC-20-006, Prepared by: Will Krantz, David Pierce, Naomi Goldenson, Danile Cayaan; November 29, 2021
4-7
Appendix G - 60
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