Groundwater use and rapid irrigation expansion in a changing climate: hydrological drivers in one of the world’s food bowls

•Water balance (1981–2015) in northwest Bangladesh to assess groundwater level falls.•Two evapotranspiration methods yield similar results capturing irrigation increase.•Trends show falls in rainfall and groundwater, evapotranspiration remains similar.•Soil permeability and groundwater recharge limit irrigation supply from soil stores.•Many factors besides irrigation expansion contribute to groundwater level falls.