The variation in groundwater level and groundwater recharge based on the rainfall received in four semi-arid districts of West Bengal, India

This article investigates the fluctuations in groundwater level (GWL) and groundwater recharge in response to rainfall variability using 2001–2021 rainfall data from four districts in West Bengal, India: Purulia, Bankura, West Midnapore, and East Midnapore. Purulia and Bankura have a tropical semi-arid to sub-humid type of climate, while West Midnapore and East Midnapore have a tropical wet-dry monsoon climate. The GWL analysis was performed using the Mann-Kendall Test (M-K Test) and Sen’s Slope Esti-mator, while groundwater recharge was estimated using empirical expressions, including the Chaturvedi and Modified Chaturvedi formulas, and the Maxey-Eakin and Krishna Rao methods. We used pre-monsoon and post-monsoon GWL data for the GWL trend analysis and monthly rainfall data for groundwater recharge estimation. To assess the impact of climate change on GWL variation for the 2022–2050 period, the global climatic model (GCM) CanESM5-SSP126 rainfall data was used. The trend analysis of ground¬water level at East Midnapore and West Midnapore shows a higher rate of decline (GWL beyond 15 m bgl) compared to Purulia and Bankura during both the pre- and post-monsoon periods. Groundwater recharge estimates increased linearly with rainfall and the results show the Modified Chaturvedi formula as the most suitable in the selected districts. Additionally, new empirical expressions developed between rainfall and groundwater levels showed a better fit for Bankura and Purulia stations. These expressions suggest that rainfall will increase in Purulia toward 2050, leading to a subsequent rise in groundwater levels.