Spatially Contrasting Groundwater Trajectories in the Indo-Gangetic Basin.

The Indo-Gangetic Basin (IGB) is a large trans-boundary aquifer system encompassing the alluvial Indo-Gangetic Plain (IGP) as well as the southern parts of the Indus, Ganges and the Rajasthan Inland drainage basin, supporting a large agrarian population. In recent decades, expansion of groundwater irrigation through shallow-medium tubewells (<70m) has boosted crop yields by reducing reliance on monsoon rains, enabling India to achieve food security and improving the livelihoods of millions. Although the IGP now accounts for around 25% of global groundwater abstraction, groundwater use in many parts of the wider IGB remains unsustainable and has driven widespread depletion. However, the Indo-Gangetic basin is not a single hydrogeological unit but a complex and heterogeneous aquifer system that is responding differently to the various pressures, including groundwater abstraction for irrigation and climate variability. Here, we analyse a groundwater well dataset to characterise the long-term patterns and trends in groundwater resources in the IGB for the time period 1998-2024, and improve our understanding of how the groundwater system interacts with various hydro-meteorological and anthropogenic factors. We compiled a new quality-controlled dataset of quarterly groundwater well data in the IGB which includes quarterly water level data for 5877 unique wells in the region. Our dataset also includes meteorological and land use data from various sources. Mann–Kendall trend analysis of groundwater levels between 1998–2010 across 2,585 wells indicates predominantly negative trends across the Indo-Gangetic Basin. These patterns can be attributed to intensification of the use of deep tubewells (>70m) in the Rajasthan Inland drainage basin and the Indus basin and shallow-medium tubewells in the Ganges basin during this period. Post-2010, we show that groundwater levels have shifted from a declining trend to a more stable trend in the Ganges basin overall. Nevertheless, in the north-west Ganges basin, Indus basin and Rajasthan inland drainage basin, despite experiencing increased rainfall and an extended multi-annual wet anomaly, groundwater levels continue to decline post-2010. The rate of decline has stabilised in the Indus basin but continues to increase in Rajasthan Inland drainage basin. In the Central Ganges basin, the trend shifts from a declining trend pre-2010 to a positive trend with rising groundwater levels. Groundwater levels in south-western parts of the Ganges basin that were stable between 1998-2010 now show a rising trend. The Minor Irrigation Census indicates no significant increase in the number of shallow–medium and deep tubewells across the Indo-Gangetic Basin between 2014 and 2017. However, land use inventory data for 2014–2024 show an expansion of cropped area in the Rajasthan Inland Drainage and Indus basins, along with an overall increase in the area sown more than once across the IGB. These patterns suggest that changes in agricultural practices, crop types and cropping patterns across sub-basins are contributing to long-term groundwater trends and variability in the region. Our results reveal pronounced, scale-dependent heterogeneity in the response of the IGB to climatic, environmental and anthropogenic stressors.