Development of Crop Coefficients for the New ASCE-EWRI Standardized Reference Evapotranspiration Model
Knowledge of evapo-transpiration (ET), or consumptive water use by agricultural crops, is important to Reclamation for hydrologic studies, water rights issues, project operations and management, and efficient use of irrigation water supplies. Reclamation operates several ET programs, including the AgriMet program in the Pacific Northwest (PN) and Great Plains (GP) regions, as well as the Agricultural Water Resource Decision Support (AWARDS)/ET Toolbox" program.
Recently, the ASCE-EWRI Technical Committee on ET developed a new standardized reference ET procedure which will soon be adopted as the world-wide standard. In order to use this reference ET procedure to model crop specific ET, crop coefficients are required. Crop coefficients are specific to the ET model, so new crop coefficients are required to use the new model in an operational mode. This proposal will fund the research required to develop these crop coefficients, making the new model useful for Reclamation.
Need and Benefit
Reclamation currently employs several methods for modeling ET: In the PN and GP regions, the AgriMet program uses the 1982 Kimberly-Penman model. Reclamation's AWARDS/ET Toolbox program
uses a Modified Penman procedure. And there are other methods used by Reclamation on a local basis throughout the Western United States. This myriad of procedures leads to misinterpretion, confusion, and lack of comparability from state to state or region to region. These differences in ET computation were recently critically examined in a court case between Colorado and Nebraska regarding Platte River water use.
Standardization of these procedures, through the implementation of the ASCE-EWRI Standardized Reference ET model, would provide several benefits to Reclamation:
* Increased comparability of ET values from region to region, state to state, etc.
* Increased acceptance of the accuracy of Reclamation's reported consumptive use values.
In order to implement this new procedure, however, new crop coefficients specific to the procedure are required. Development of these crop coefficients is the purpose of this Science and Technology (S&T) research project.
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