A study published recently in PNAS reports the future of water-level rise in the Ganges-Brahmaputra-Meghna delta. A collaboration of researchers from the CNRS, IRD, BRGM, La Rochelle Université, Université des Antilles and Bangladesh University of Engineering and Technology warns that water levels will rise 85 to 140 cm by 2100, depending on the region of the delta.
The Ganges-Brahmaputra-Meghna delta is the largest and most densely populated delta in the world, covering eastern India and two-thirds of Bangladesh. With over 1000 inhabitants per km², intense monsoon rainfall, flooding, rising sea levels, and land subsidence threaten those that live within. Nevertheless, to date, insufficient research has been carried out to determine the extent and impact of water-level rise. This study aimed to rectify this and provide recommendations for future investigations and management strategies.
In order to do so, the collaborating researchers looked at monthly readings from 101 gauges measuring water and sea levels across the region from 1968 to 2012. They found that water level in the delta increased more than the global mean sea level rise, at 3 mm/year on average, compared to 2 mm/year.
The team also considered the impact of land subsidence. Land subsidence refers to the lowering of the land level. Previous estimates had put land subsidence measurements at 1-2 cm/year in some regions, but the findings from this study show maximum land subsidence in the delta between 1993 and 2012 as between 1 and 7 mm/year. The precision of this reading is important to clarify, as it acts as a reference point that can be used to monitor water level rise.
According to these findings, the researchers predict that should land subsidence continue at the same rate, water-level rise by 2100 will reach 85-140 centimeters. Given that these numbers are double the IPCC report’s projections (which did not consider land subsidence as a factor), the authors hope that their research will aid in ameliorating water-level rise forecasts within the delta, providing preparation and protection for the 200 million people who call it home.