ABSTRACTION-TRIGGERED LONG TERM GROUNDWATER STORAGE DEPLETION IN PARTS OF THE GANGES BASIN OF THE INDIAN SUBCONTINENT

Exponential increase in population triggers significant depletion in groundwater storage (GWS), particularly in the developing countries like India, due to the demands of irrigation and industry. Approximately, 70% of groundwater withdrawals worldwide are associated with irrigation. In order to study long-term GWS change over parts of the Indian subcontinent, we used Gravity Recovery and Climate Experiment (GRACE) data. Monthly mean liquid water equivalent thickness data files from the GRACE RL05 dataset were retrieved from NASA-JPL archive and analyzed. Change in liquid water equivalent thickness total changes in GWS, soil moisture, and surface water components. The latter two components can be estimated using global-scale hydrological model output from the GLDAS dataset. Our study of interannual (2003 to 2012) GWS change reveals rapid depletion (>1 cm/year) in the northern and eastern parts of Indian subcontinent, particularly on the areas of Ganges river basin (mostly India and Bangladesh), which hosts the densest population of the planet. The fertile alluvial plains of the Ganges river are also extremely conducive for agricultural activities thus making it the “bread basket” of southeast Asia, which in turn also demands rapid increase in groundwater abstraction with the increasing population and introduction of water-intensive crops (e.g. boro rice). Consequently, groundwater abstraction rates peaked in recent years. Seasonal groundwater levels are lowest during the pre-monsoon season. Our estimates are consistent with the field water level measurements in recent years (n> 1,000, r² >0.85). In addition, inter-annual precipitation variability plays a key role in controlling GWS changes over the north India plains. However, within the last decade, no trend in variability of precipitation was observed in the area exhibiting maximum groundwater depletion.