The impact of climate change on regional water balances in Bangladesh

Abstract

The probable effect of climate change on the water available for use in Bangladesh is not well known. We calculate monthly water balances for five main regions of Bangladesh to examine the likely impacts of climate change to 2050. We also examine the impact of past and potential future irrigation development. Climate change projections for rainfall in Bangladesh are uncertain, with increased rain in the wet season likely, but decreased rain also possible. Runoff is projected to vary in a manner similar to rainfall. However, assuming no change to the area of crops, all projections result in increases in irrigation water use, which leads to groundwater level declines. The impact of change (whether climate change or development) on water availability and use is greater in the Northwest region than elsewhere. For most water balance terms in most regions, irrigation development (both historic and future) is calculated to have a larger impact than climate change. Climate change is calculated to have a larger impact than irrigation development only on evapotranspiration and runoff, and possibly on groundwater levels. Model sensitivity tests suggest that model uncertainty is less than climate change uncertainty. To reverse lowered groundwater levels, Bangladesh’s policy includes greater use of surface water. While we calculate groundwater levels will rise, the viability of the policy may be affected by future changes to upstream use.