Modelling the impacts of climate change and management options on sustainable groundwater use in an irrigated agriculture landscape

Declining groundwater resources are a big concern for irrigated agriculture worldwide. This study investigated the causes of declining groundwater and how future climate and management measures impact the groundwater resource in Bangladesh. A conceptual hydrological model (NAM) was used to quantify catchment runoff, groundwater recharge and evapotranspiration loss and a hydraulic model (MIKE11) was used to quantify changes in river flow. The models were calibrated using observed water level, discharge, groundwater level (GWL) and actual evapotranspiration (ET). The modelling encompassed five contrasting climate scenarios of rainfall and potential evapotranspiration (PET) and a management scenario of additional surface water irrigation. The results show that GWL is declining across 16 administrative districts in the northwest region of Bangladesh. On average, the annual decline varies from 20 to 30 mm except for two southern districts where the annual decline was more than 80 mm. Declining rainfall and increasing use of groundwater for irrigation were the principal causes of declining GWL across the region. Under the climate change scenarios, modelled groundwater conditions improve due to increased rainfall. The increase in river water extraction for irrigation also produced positive outcomes for GWL (i.e., lessening the declining rate).