SPATIAL UNIFORMITY IN SENSITIVITY COEFFICIENT OF REFERENCE ET IN THE TEXAS HIGH PLAINS
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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 crop ET 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 variables 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 variables 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 variables. 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 variable (e.g., wind speed) across the region showed no significant differences in the sensitivity of reference ET to those variables by location. This indicates that the existing North-South air temperature gradient and variability in local wind circulation patterns have limited influence on the sensitivity of reference ET to individual weather variables. This indicated that a uniform maintenance protocol should be sufficient for weather stations located throughout the Texas High Plains.
