Mapping Crop-Specific Drought Index for Groundwater Management in the Texas High Plains.

Drought is a highly destructive natural phenomenon that affects portions of the U.S. almost every year. Moisture deficiencies can become catastrophic for agriculture and crop yields. Of the numerous drought indicators currently being used, the most popular indices include the Palmer Drought Severity Index (PDSI), the Standardized Precipitation Index (SPI), and the U.S. Drought Monitor.  These indices, however, may not be best suited for monitoring agricultural drought to assist in groundwater management. Evapotranspiration (ET) is an important component in the agricultural water budget; thus, it is necessary to include ET in agricultural drought monitoring.  The PDSI and U.S. Drought monitor require many input parameters including soil moisture, which can be difficult to obtain, while the SPI provides only deviation of precipitation from normal levels. In response to these limitations, the Standardized Precipitation-Evapotranspiration Index (SPEI) was recently introduced to monitor agricultural drought. The SPEI uses the difference between precipitation and reference ET, which is an indicator of crop water deficiency or irrigation demand. In this study, crop-specific monthly SPEI drought index maps for the Texas High Plains were developed using Texas High Plains ET (TXHPET) network data. Additionally, statistical relationships between crop-specific SPEI and irrigation demand were evaluated to determine their ability to assist in groundwater management in the Texas High Plains.