Groundwater balance and long-term storage trends in the regional Indo-Gangetic aquifer in northwest Bangladesh

Study Region: The study region is the northwest region of Bangladesh Study Focus: The study focuses on developing an improved understanding of groundwater balance and long-term groundwater storage trends in the districts of northwest Bangladesh. We used MODFLOW-2005 to construct two groundwater models of northwest Bangladesh, which differed in the conceptual representation of groundwater recharge to investigate groundwater balance and storage trends. One approach was based on estimating gross recharge and the other on estimating net recharge by ignoring direct use of groundwater by vegetation. The two models were calibrated by fitting to observed groundwater levels, with a probabilistic method using PEST-IES, resulting in 500 realisations of comparable goodness of fit for each model. New Hydrological Insights for the Region: The two modelling approaches provided plausible range of groundwater storage decline in the northwest region with long-term average between − 1.1 mm/y and − 5.3 mm/y. In the southern parts of the region groundwater storage is declining with highest rates of − 12.5 mm/y, − 10.6 mm/y and − 8.9 mm/y respectively in Nawabganj, Naogaon and Rajshahi respectively. Groundwater use appears to be unsustainable in this area. The northern part receives greater rainfall, and groundwater storage is declining less. Furthermore, the recharge rates are less than the potential rates. In this part of the region, some further development of groundwater use may be sustainable