A drought index based on actual evapotranspiration from the Bouchet hypothesis

Global drought assessment has mainly depended on precipitation-based drought indices that may also take into account potential evapotranspiration (ET_p). In this study, we combined the actual evapotranspiration (ET_a) estimated from the Bouchet hypothesis and the structure of the Standardized Precipitation-Evapotranspiration Index to develop a fully ET-based drought index, the Standardized Evapotranspiration Deficit Index (SEDI). We found that SEDI, without using precipitation data, produces results that are consistent with the Palmer Drought Severity Index (PDSI) and the Standardized Precipitation Index (SPI) for drought identification in the South-Central United States. We also found a competitive performance of SEDI through comparisons between the Vegetation Health Index with SEDI, PDSI, and SPI. We suggest the high applicability of the SEDI based on the Bouchet hypothesis as an independent drought index for regions with strong land-atmosphere coupling or as an alternative drought index to fully precipitation-dependent indices for assessing agricultural droughts.