Sustainable groundwater use in the Eastern Gangetic Plains requires region-specific solutions

This study aimed to examine whether conservation agriculture can be applied across the Eastern Gangetic Plains (EGP) as a strategy to ensure that groundwater use for irrigation remains sustainable as demands increase. The study analysed the groundwater balance in the EGP at sub-region, district and field scales using MODFLOW, a water balance model, and the APSIM model, respectively and evaluated the current state of groundwater development aiming to address sustainability concerns. Long-term groundwater use and aquifer reserves reveal the significant influence of groundwater extraction on the current state of the water balance. In the Indian and northwest Bangladesh sub-regions, accelerated extraction may result in groundwater mining in areas where potential maximum recharge has already been achieved or exceeded, while further development of groundwater may be possible in areas where actual recharge is still less than potential recharge. At district level, the water supply versus demand situation shows a large annual surplus in the East but a deficit in the West. Conservation Agriculture (CA) and Alternate Wetting and Drying (AWD) irrigation practice exert varying impacts on water demand; crop transpiration (Ep) is generally higher in CA compared to Conventional Tillage (CT), while soil evaporation (Es) is similar in both practices. Net evapotranspiration, although very similar in both practices, is generally greater in CA. AWD has a limited effect on Es but reduces the percolation rate and therefore irrigation requirement of Boro rice. In conclusion, the cause–effect associations between irrigation water use and groundwater sustainability are not spatially uniform across the EGP, nor will they likely be so under further agricultural development associated with increased water demands. The study suggests that the cause–effect interactions between irrigation water use and groundwater sustainability cannot be generalized across the EGP and, therefore, CA or AWD should not be applied uniformly across the region.