Drought characterization using the Combined Terrestrial Evapotranspiration Index over the Indus, Ganga and Brahmaputra river basins

Abstract

Drought is a recurring natural disaster, which significantly affects the economy and environment of diverse geographical area worldwide. Therefore, it is imperative to develop a new technique that enables comprehensive identification and monitoring of drought over a large spatial extent. In this study, a new drought index called Combined Terrestrial Evapotranspiration Index (CTEI) is developed by using a combination of Gravity Recovery and Climate Experiment (GRACE) data and meteorological parameters, i.e. precipitation (P) and potential evapotranspiration (PET) over the Indus, Ganga, and the Brahmaputra (IGB) river basins. Further, the results of CTEI are compared with pre-existing drought indices, which highlighted good correlation with GRACE Groundwater Drought Index (GGDI) (ρ = 0.88), Water storage deficit index (WSDI) (ρ = 0.96), Combined Climatologic Deviation Index (CCDI) (ρ = 0.97) and Standardized Precipitation-Evapotranspiration Index (SPEI) (ρ = 0.49). It also compared with In-situ Groundwater Drought Index (IGDI) derived by groundwater observation wells. The mean annual CTEI exhibited a strong correlation with IGDI (0.49 to 0.77) and climatic parameters (P, PET, and land surface temperature). Outcomes illustrated a significant potential of CTEI index and extended the utility of GRACE derived Terrestrial Water Storage observations for drought characterization as well as quantification of its severity.