ASSESSMENT OF GROUNDWATER VARIABILITY AND DROUGHT VULNERABILITY IN THE GANGA BASIN USING GRACE/FO AND METEOROLOGICAL DATA

Abstract

The Ganga basin is India's most densely populated and water-stressed river basin, contributing significantly to 40% of the country's gross domestic product. Given its immense cultural, heritage, and economic significance, assessing the variability in groundwater and drought conditions across the basin becomes crucial. The study investigates changes in subsurface groundwater storage from January 2003 to December 2022, utilising datasets from the Gravity Recovery and Climate Experiment, Global Land Data Assimilation System, and India Meteorological Department. It offers valuable insights into regional and basin-level hydrological variability while assessing drought phases using the Groundwater Drought Potential Index across all 19 sub-basins. This analysis aims to understand fluctuations in groundwater storage associated with spatiotemporal variation, depletion trends, pre- and postmonsoon analysis, potential drought occurrences and drought events within the Ganga basin and its sub-basins. Consequently, utilising the above datasets, this study estimates a decline in terrestrial water storage and groundwater storage at approximately -1.54 cm/year and -1.52 cm/year, respectively, over the entire study period. Furthermore, the analysis indicates a depletion of approximately 258.91 cubic kilometres of groundwater within the Ganga basin. It also highlights that the Ganga basin experienced drought conditions for 74 out of 240 months, spanning over 10 drought events during the study period. Notably, the Yamuna upper sub-basin stands out with the most negative trends of -5.45 cm/year and -5.65 cm/year for Terrestrial Water Storage Anomaly and Groundwater Storage Anomaly, respectively, alongside a groundwater volume change rate of -1.74 km3/year. The estimation of drought potential amount indicates that the groundwater recharge requirement for the Ganga basin is approximately 193.58 cm annually, partially met by an annual precipitation of 102.32 cm. Consequently, the annual drought potential amounts to 91.25 cm.