Impacts of long-term droughts on available terrestrial water in the major river basins of the world

Long-term droughts significantly impact the terrestrial water resources in the world, however, observed changes in major river basins have not been well explored. Here we use the Standardized Precipitation Evapotranspiration Index (SPEI) at four different time scales (12, 24, 36, and 48 months) to identify long-term droughts in the world from 1901 to 2018. For this study, we select the 26 major river basins in the world. We use the data from the Gravity Recovery and Climate Experiment (GRACE) to estimate the changes in terrestrial water storage (TWS) from the last 20 years (20022021). We evaluate the linkage between GRACE TWS and long-term droughts based on SPEI for the major basins during 2002-2021 to understand the impacts of droughts on water availability in the world. We compare major droughts characteristics in the selected major river basins. We found a negative trend of global TWS from 2002 to 2021. SPEI at longer time scales is positively associated with TWS indicating the adverse impacts of droughts on surface and groundwater resources in such a populated region. Keywords: Drought, Standardized Precipitation Evapotranspiration Index (SPEI), the Gravity Recovery and Climate Experiment (GRACE), terrestrial water storage (TWS)