USE OF CROP-SPECIFIC DROUGHT INDICES FOR DETERMINING IRRIGATION DEMAND IN THE TEXAS HIGH PLAINS

Drought is a highly destructive natural phenomenon that affects portions of the United States almost every year. Severe water deficiencies can become catastrophic for agriculture and crop yields. Evapotranspiration (ET) is an important component in the agricultural water budget; thus, it is strongly preferred to include ET in agricultural drought monitoring. Consequently, the Standardized Precipitation-Evapotranspiration Index (SPEI) was recently introduced to monitor agricultural drought. In this study, statistical relationships between crop-specific monthly SPEI and corresponding irrigation demand were developed using Texas High Plains ET (TXHPET) network data and evaluated for determining their usefulness in groundwater management within the Texas High Plains. Based on the precipitation gradient and availability of the data within the Texas High Plains, five counties were selected for calculating monthly SPEIs for the period of 1997-2010. The SPEI methodology was found to be easy to implement. Strong relationships were found between crop-specific SPEI and irrigation demand in all five counties with R-2 values ranging from 0.87 to 0.99, which indicated that these regression models have the potential to be used as tools to estimate county-wide irrigation demand