BUSHLAND REFERENCE EVAPOTRANSPIRATION CALCULATOR Prasanna H. Gowda 1 Terry A. Howell 1 Jerry Ennis 1* Thomas H. Marek 2 Dana O. Porter 3 Research Agricultural Engineer Research Agricultural Engineer IT Specialist Research Agricultural Engineer Associate Professor & Acting Laboratory Director *Presenting Author 1 USDA-ARS Conservation and Production Research Laboratory, Bushland, TX; 2 Texas AgriLife Research & Extension, Amarillo, TX; 3 Texas AgriLife Research & Extension, Lubbock, TX REFERENCES Accurate daily reference evapotranspiration (ET) values are needed to estimate crop water demand for irrigation management and hydrologic modeling purposes. The Bushland Reference ET Calculator was developed by the USDA-ARS Conservation and Production Research Laboratory at Bushland, Texas for calculating hourly and daily grass and alfalfa reference ET. The user-friendly interface for the calculator was developed using.NET programming. The calculator uses the ASCE Standardized Reference Evapotranspiration (ET) Equation for calculating both grass and alfalfa reference ET at hourly and daily time steps. Users have the option of using a single set or time series weather data to calculate reference ET. Daily reference ET can be calculated either by summing the hourly ET values for a given day or by using daily averages of the climatic data. Although the Bushland Reference ET Calculator was designed and developed for use mainly by producers and crop consultants to manage irrigation scheduling, it can also be used in educational training, research, and other practical applications. This paper demonstrates use of the Bushland Reference ET Calculator that being distributed through the USDA-ARS web site to interested users at no cost. HOURLY AND DAILY ET FROM HOURLY INPUT – TIME SERIESHOURLY ET – SINGLE CALCULATION DAILY ET FROM DAILY INPUT – TIME SERIESHOURLY ET – SINGLE CALCULATION BUSHLAND REFERENCE ET CALCULATOR – FRONT PAGE ONGOING WORK – iPhone APPLICATION DEVELOPMENT ABSTRACT BACKGROUND In agriculture, evapotranspiration (ET) is a major consumptive use of irrigation water and precipitation. Any attempt to improve water use efficiency must be based on reliable and accurate estimates of ET or crop water use, which includes water evaporation from land and water surfaces and transpiration by vegetation. Crop-specific crop water use can be estimated by multiplying reference ET calculated from meteorological data by an appropriate crop coefficient derived from lysimeter studies (Marek et al., 2010). However, the ASCE-EWRI standardized reference ET equation is very complex to use. Recently, it was identified by the ASCE-EWRI ET Task Committee that currently there exists a need for a mobile, user-friendly ET calculator targeting advanced producers and crop consultants. For nearly 20 years in the Texas High Plains, daily reference ET and crop water use data were provided on a daily basis to producers and crop consultants by the Texas High Plains ET Network at no cost. However, this service was recently terminated due to the lack of funding support. Therefore, there is an immediate need for a simple reference ET calculator that can be used by crop consultants and producers to estimate accurate reference ET and representative crop water use with locally available weather data for irrigation scheduling purposes, thereby implementing the latest water conservation and best management practices. Allen, R.G., Walter, I.A., Elliott, R., Howell, T., Itenfisu, D., and Jensen, M. (Eds.) The ASCE standardized reference evapotranspiration equation. Environmental and Water Resources Institute of the American Society of Civil Engineers, Reston, Virginia. Marek, T.H., T.A. Howell, R.L. Synder, D. Porter, and T. Scherer Crop coefficient development and application to an evapotranspiration network ASABE-IA Fifth Decennial Symposium, Phoenix, AZ, Texas AgriLife Research at Amarillo, AREC p. APPROACH Reference ET Calculations: ASCE-EWRI Standardized Reference Evapotranspiration (ET) Equation (Allen et al., 2005) was used for calculating both grass and alfalfa reference ET at hourly and daily time steps. A more complex equation provided in the Appendix D of the ASCE-EWRI ET manual was used for estimating clear-sky solar radiation. Daily reference ET can be estimated either by summing the hourly ET values for a given day or by using daily averages of the climatic data. Calculator Design and Development: Bushland Reference ET Calculator was developed using the Visual Basic Programming language in.NET environment. Efforts are made to design the interactive pages for more intuitive data input. In single calculation interactive pages, errors flags are added to identify invalid or missing data. Sample input and output files are provided with the calculator for time series calculations to assist users with input and output formats. Bushland Reference ET Calculator can be downloaded from the USDA-ARS Conservation and Production Research Laboratory’s website at: Bushland Reference ET Calculator can be downloaded from the USDA-ARS Conservation and Production Research Laboratory’s website at: