Changes in Hydrology of the Ganges Delta of Bangladesh and Corresponding Impacts on Water Resources

Abstract

The Ganges Delta in Bangladesh is an example of water‐related catastrophes in a major rural river basin where limitations in quantity, quality, and timing of available water are producing disastrous conditions. Water availability limitations are modifying the hydrologic characteristics especially when water allocation is controlled from the upstream Farakka Barrage. This study presents the changes and consequences in the hydrologic regime due to climate‐ and human‐induced stresses. Flow duration curves (FDCs), rainfall elasticity, and temperature sensitivity were used to assess the pre‐ and post‐barrage water flow patterns. Hydrologic and climate indices were computed to provide insight on hydro‐climatic variability and trend. Significant increases in temperature, evapotranspiration, hot days, heating, and cooling degree days indicate the region is heading toward a warmer climate. Moreover, increase in high‐intensity rainfall of short duration is making the region prone to extreme floods. FDCs depict a large reduction in river flows between pre‐ and post‐barrage periods, resulting in lower water storage capacity. The reduction in freshwater flow increased the extent and intensity of salinity intrusion. This freshwater scarcity is reducing livelihood options considerably and indirectly forcing population migration from the delta region. Understanding the causes and directions of hydrologic changes is essential to formulate improve water resources management in the region.

Geomorphic change in the Ganges–Brahmaputra–Meghna delta

“…During the last century, large-scale artificial changes, such as river diversions, upstream dams, excavation of canals, land reclamation projects and the polderisation (embanking) of the coastal zone 41 have disrupted the morphological equilibrium of the delta (Figure 3) 54 . In 1975, India commissioned a barrage on the main Ganges River at Farakka (Figure 1) to divert approximately 60% of the dry season flow towards the Bhagirathi-Hooghly River to make the Kolkata Port navigable [55][56][57] . This controlled hydro-geomorphological regime has dramatically altered natural processes in the southwest Ganges-dependent region, changing channel dynamics and resulting channel planforms and geometries [58][59][60] .…”

“…The Gorai River (Figure 1), the main distributary of the Ganges flowing to south-west Bangladesh, has seen a notable increase in siltation [G] due to reduced river capacity to carry sediment 56,61,62 , as the majority of dryseason flow has been diverted to the Bhagirathi-Hooghly River. In some areas along the Gorai, this siltation has led to the development of charlands [G].…”

“…The upstream reaches of the Mathabhanga River have completely dried up. This reduction in freshwater flow has not only altered the geomorphic behaviour of the Ganges downstream of the Barrage, but also caused dry-season salinity in the south-west of Bangladesh to increase by an order of magnitude 56,62 , which has impacted the state of the Sundarban mangrove forest ecosystem and local livelihoods 61,63 . The reduced dry-season flow in the Ganges has also altered groundwater recharge and resulted in micro-climatic and agro-ecological changes along the lower Ganges River 64 .…”

“…The rivers have been disconnected from their floodplains, preventing tidal and fluvial sediment from infilling the embanked land 8,11 . This disconnection has not only lowered the relative elevation of the deltaic floodplains, but has also exacerbated the silting up of channels and increased sediment deposition further into the bay 8,17,41,54,56,68 . The deltaic dynamics at present are therefore a complex interplay of background natural responses to long-term change, and shorter-term responses to considerable anthropogenic activities 69 .…”

Featured Collection Introduction: Climate Change Solutions

“…Their analysis shows a 2–3 times increase in 24‐ and 48‐h precipitation intensity indicated an increase of up to 50% increase in flood flows are likely in the future. Murshed et al () study hydro‐climatic trends in the Ganges delta of Bangladesh — a low‐lying, high‐density island on the verge of water‐related catastrophe. Using available observed data, they demonstrate intensification of rainfall events and associated flooding in this otherwise water‐scarce region.…”