Impact of potential and actual evapotranspiration on drought phenomena over water and energy-limited regions

Understanding the relevance of potential (PET) and actual evapotranspiration (AET) in the drought characterization over energy and water-limited regions is unexplored. The present study tries to restructure the Standardized Precipitation Evapotranspiration Index (SPEI) with AET to represent the anomalies of actual water availability in addition to precipitation over India. The AET is estimated using the Budyko hypothesis at annual scale which was validated with Global Land Evaporation Amsterdam Model (GLEAM) satellite-based AET data. AET-based drought index was in more agreement with remote sensing-based drought severity index (DSI) for major drought events compared to PET-based drought index for water-limited zone compared to energy-limited. For water-limited zones, the PET-based drought index has overestimated the drought intensities, while for energy-limited zones such effect is not significant. AET-based drought index has estimated lesser areal extents under extreme drought conditions compared to PET-based drought index for water-limited zones of India. The rate of increase of drought frequencies was noted to be higher with AET for extreme droughts when compared to other categories. Overall, considerable differences in drought characteristics based on PET and AET drought indices over water-limited zones of India stresses on the use of AET in the drought assessment instead of PET.