|PORTER, DANA - Texas Agrilife Extension|
|MAREK, THOMAS - Texas Agrilife Research|
|HOWELL, TERRY - Retired ARS Employee|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2015
Publication Date: 4/27/2016
Citation: Moorhead, J.E., Gowda, P., Marek, G.W., Porter, D.O., Marek, T.H., Howell, T.A. 2016. Spatial uniformity in sensitivity coefficient of reference ET in the Texas High Plains. Applied Engineering in Agriculture. 32(2):263-269:doi:10.13031/aea.32.10940.
Interpretive Summary: Supplies of fresh water for irrigation are decreasing because of demand for other uses, hydrology or water policies, creating an environment in which agriculture needs to be water-smart. Reference evapotranspiration (ET, water use for a well-watered reference crop) is widely used to estimate crop ET for optimum irrigation scheduling. Accurate measurements of weather parameters are important for profitable irrigated crop production. Better understanding of the spatial variability in the sensitivity of reference ET to weather parameters is needed for designing and operating regional ET networks more efficiently. Scientists at the USDA-ARS (Bushland, TX) studied the sensitivity of reference ET to weather parameters throughout the Texas High Plains. Results indicated that there were no significant differences in the sensitivity of reference ET to weather parameters and therefore, a single standard maintenance protocol is sufficient to maintain the weather network in the Texas High Plains.
Technical Abstract: Evapotranspiration (ET) is a major component of the agricultural water budget and accurate ET estimations are essential for effective irrigation scheduling. Therefore, it is an important aspect of production agriculture and agricultural research. Potential ET of a crop can be calculated by multiplying reference ET by an appropriate crop coefficient. Reference ET can be estimated from meteorological data obtained from weather stations sited on a reference crop surface, e.g. grass or alfalfa. However, weather station sensor inaccuracies may propagate measurement errors into the reference ET calculations. A sensitivity analysis of weather parameters used in calculating ET (air temperature, wind speed, solar radiation, and relative humidity) can be used to determine relative effects of data inaccuracies on ET estimates, and conversely, the sensor accuracy levels needed for acceptably accurate ET estimates. In this study, sensitivity analyses of weather parameters on daily reference ET were conducted using hourly data (1995-2008) from eight weather stations managed by the Texas High Plains ET network in the Texas Panhandle. Sensitivity coefficients were calculated for each of the weather parameters. Comparison of the sensitivity coefficients for any one station indicated that reference ET was most sensitive to wind speed followed by air temperature. Comparison of sensitivity coefficients for any one weather parameter (e.g. wind speed) across the region showed no significant differences in the sensitivity of reference ET to those parameters by location. This indicates that the existing N-S air temperature gradient and variability in local wind circulation patterns have limited influence on the sensitivity of reference ET to individual weather parameters.