The following computer application programs have been cooperatively developed and released by DWR and the University of California, Davis.
The CUP+ program is a Microsoft Excel application that estimates crop evapotranspiration (ETc) and evapotranspiration of applied water (ETaw). ETaw is a seasonal estimate of the irrigation water requirement for evapotranspiration of a crop minus any water supplied by effective rainfall and effective seepage. ETaw information is needed to determine the demand side of water requirements. In addition to using monthly climate data, the program uses daily measured weather data to estimate daily soil water balances for surfaces that account for evapotranspiration losses and water contributions from rainfall, seepage, and irrigation. Soil water-holding characteristics, effective rooting depths, and irrigation frequency are used with rainfall and ETc data to calculate a daily water balance and determine effective rainfall and ETaw, which is equal to the seasonal cumulative ETc minus the effective rainfall. The application outputs a wide range of tables and charts that are useful for irrigation planning. It also can be used to study the impact of climate change on evapotranspiration and irrigation water needs.
(CUP+ pamphlet (PDF))
The Simulation of Evapotranspiration of Applied Water (SIMETAW) program was developed to help water planners and researchers to improve their long term estimates of net crop water requirements. This program can simulate many years of weather data from monthly climate data and use the simulated data to estimate reference evapotranspiration (ETo) and ETc. In addition, simulated daily rainfall, and soil crop information are used to determine effective rainfall and ETaw, where ETaw is an estimate of the crop evapotranspiration minus any water supplied by effective rainfall. The simulation program allows one to investigate how climate change might affect water demand. In addition, the use of the widely adopted Penman-Monteith equation for ETo and improved methodology to apply crop coefficients for estimating crop evapotranspiration is used to improve ETaw accuracy.
(SIMETAW pamphlet (PDF))
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.
Cal-SIMETAW Journal Article (PDF)
California Weather Data - The California Weather Data program was developed in Microsoft Excel to provide daily mean weather and ETo data from CIMIS to input into the CUP and SIMETAW models. (xls: 3.52 MB - 635 KB ZIP)