Shift in groundwater recharge of the Bengal Basin from rainfall to surface water

Groundwater supports agriculture and provides domestic water for over 250 million people in the Bengal Basin. Here we investigate the source of groundwater recharge using over 2500 stable water isotope measurements from the region. We employ a Monte Carlo statistical analysis to find distributions of possible components of recharge by accounting for the variability of isotope ratios in each of the possible recharge sources. We find that groundwater recharge sources have shifted in the last decades with a similar to 50% increase in recharge from stagnant surface water bodies (mostly during the latter part of the dry season) and a relative decrease in contribution from direct infiltration of precipitation (which occurs mostly in the early monsoon). We attribute this shift to an increase in standing water in irrigated rice fields and ponds, and an increase in the downward hydraulic gradient during the dry season driven by pumping.

Automated summary

In this study, we investigated the source of groundwater recharge in the Bengal Basin using stable water isotope measurements. Through Monte Carlo statistical analysis, we found distributions of possible recharge sources by considering the variability of isotope ratios. Our results show that there has been a shift in groundwater recharge sources in recent decades, with an increase in recharge from stagnant surface water bodies and a decrease in direct infiltration of precipitation. This shift is attributed to an increase in standing water in irrigated rice fields and ponds, as well as an increase in the downward hydraulic gradient during the dry season driven by pumping.