Bangladesh Integrated Water Resources Assessment supplementary report: approximate regional water balances

[摘要] The overall water balance for Bangladesh is not well known. The recharge to aquifers has not been quantified, except in a few small districts. The overall use of groundwater by irrigation has not been quantified, and this use has not been compared to recharge to test notions of sustainability. We develop approximate water balances for each of the main regions of Bangladesh (excluding the Chittagong hill tracts). The water balances bring together current information on rainfall, crop areas, evapotranspiration, groundwater levels and river flow to form approximate water balances for each region. The regional water balances are for the water resources internal to each region and do not include the major rivers – the Ganges, Jamuna (the name for the Brahmaputra in Bangladesh) and Meghna. We use the approximate water balances to assess the likely regional responses (at least in direction, if not in absolute magnitude) to changes in water availability under climate change and management to substitute surface water use for irrigation with groundwater. Climate change projections are uncertain, with increased rain in the wet season likely, but decreased rain also possible. The projections with more rain may lead to increased recharge and runoff, and increased water availability. However, increased projected potential evapotranspiration may also lead to increased irrigation requirement. Climate variability, at least to 2050, is projected to have a greater impact on regional water balances than climate change. The increased use of surface water, particularly when combined with an increase in irrigation overall, may lead to greater recharge and some restoration of groundwater levels. As a result, it may also lead to greater baseflows from groundwater to the rivers (so some of the water pumped from the rivers in effect recycles back to the rivers). The simple and approximate water balances developed here should be refined through further studies.

[发布机构] CSIRO

[学科分类] 地球科学(综合)