Statewide models and tools

The California Department of Water Resources (DWR) , through the California Water Plan, uses a number of tools to support water management in California. Among these tools are the Water Portfolios, Future Scenarios, and Cal-SIMETAW. Water Portfolios show water uses and supplies for 1998-2015. Future Scenarios ask different questions and develop analytical approaches to evaluate future water management conditions. Cal-SIMETAW is the California application of the SIMETAW model, which is a land surface model that specializes in estimating the evaportranspiration and applied water of various crops.
Water Portfolios through a set of workbooks and flow diagrams  provide an accounting of all water that enters and leaves the state and how water is used and exchanged among California’s 10 hydrologic regions. Understanding Water Portfolios is important for water planning activities conducted by the State as well as by various regional and local water agencies. Data from Water Portfolios also enable comparison of the variation of water uses and sources of supply  for wet, average, and dry hydrologic conditions for each hydrologic region. The statewide information is developed by aggregating data from the 10 hydrologic regions.

The California Water Plan uses multiple future scenarios and alternative response packages as an analytical approach to evaluate future water management conditions. The scenarios are not meant to be forecasts of the future, but represent alternative plausible conditions for the future. Response packages to these scenarios comprise different mixes of resource management strategies.

Scenarios are shaped by factors considered to be beyond the control of water managers. Each scenario has alternative values for factors such as land use, population growth and density, and climate change. Water Plan scenarios are used to explore questions about the plausible futures; for example, what will the year 2050 be like if California's population continues to grow at the rate it has over the past several years, and what if the rate increases over the next 10, 20, or more years? How will shifting land use influence future water demands for agriculture or municipalities? Similarly, how will climate change as simulated by various Global Climate Models will affect demands and supply, and how the overlay of climate change, land use, and population growth and density play out in tandem?


The Cal-SIMETAW model was designed to estimate daily soil water balance to determine ETc and ETaw for use in the California Water Plan Update. The model requires weather data, soils, crop coefficients, rooting depths, seepage, etc., that influence crop water balance. The model uses daily weather data, derived from monthly PRISM climate data and daily U.S. National Climate Data Center climate station data to cover California with 4×4 km grid spacing. From the PRISM data, ETo is estimated using the Hargreaves-Samani equation that was calibrated to estimate regional Penman-Monteith equation ETo to account for spatial climate differences. In addition to using historical data, Cal-SIMETAW can use near-real-time data from Spatial CIMIS, which is a model that combines weather station data and remote sensing to provide a statewide grid of ETo information. The model uses SSURGO soil characteristic data and crop information with precipitation and ETc data to generate hypothetical water balance irrigation schedules to determine ETaw, which is an estimate of the seasonal irrigation requirement assuming 100% application efficiency. Cal-SIMETAW also has the ability to generate daily weather data from monthly mean values for use in studying climate change scenarios and possible impacts on water demand.

We provide technical assistance and policy guidance for economic and demographic analyses to sustainably manage California’s water resources. In addition to developing economic and demographic models and tools our work includes:

  • Analyzing local, regional, and statewide economic costs and benefits of proposed water management programs and projects and determining socioeconomic impacts
  • Determining the economic values of ecosystem services
  • Using GIS and other methods to allocate current and forecasted demographic data, including population, housing, and personal income to geographic areas
  • Forecasting economically based urban and agricultural water demands
  • Evaluating regional and statewide direct and indirect economic impacts of water shortages
  • Estimating the value of changes to urban and agricultural water supply reliability
  • Providing technical assistance to state, federal, and local agencies