Water level rise in Ganga-Brahmaputra delta could reach 85-140 cm by 2100

Water level rise in the Ganga-Brahmaputra-Meghna delta could reach 85 to 140 cm by 2100, found researchers in a latest study amid rising concerns over the effects of climate change in the world’s largest delta regions.

Situated north of Bay of Bengal, the Ganga-Brahmaputra-Meghna delta covering two-thirds of Bangladesh and part of West Bengal, India is the largest and most densely populated deltas in the world. It is also one of the most vulnerable to climate-driven sea-level rise and monsoon flooding presenting a major challenge for climate change adaptation of its 200 million inhabitants.

Sunderbans, world’s largest Mangrove forest is a key area in the region.

Researchers from France and Bangladesh who carried out the study found that between 1968 and 2012, the water level in the delta increased faster by 3 mm/year on average, slightly more than global mean sea level (∼2 mm/year) during the same period. And, 2005 onwards, the water level rise was faster towards the west of the delta.

They also estimated the contribution of land subsidence (the gradual sinking of the earth’s surface to the rise of water level) which can exacerbate the effects of sea-level rise and found that maximum land subsidence in the delta during 1993 and 2012 was between 1 and 7 mm/year.

“If subsidence continues at the same rate through the century, the water-level rise, could reach 85 to 140 cm, by 2100 compared to the period 1986-2005. This is double the rise previously projected under a greenhouse gas emission mitigation scenario in UN’s Inter-governmental Panel of Climate Change (IPCC) report,” warns the study.

The findings published in journal PNAS, could help improve forecasts of water level in the region, home to 200 million people and lead to future impact studies and possible adaptation plans in wake of the rising impacts of climate change.

Researchers also explain that the fluctuations in the water-level each year were strongly modulated by the ocean phenomenon called the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) variability’. “Water level was lower than average by 30 to 60 cm during co-occurrent El Niño and positive IOD events and higher-than-average water level, by 16 to 35 cm, during La Niña years,” stated the study.

The study was conducted by analyzing monthly readings from 101 gauges measuring water and sea levels across the delta. The data was then aggregated over geographical areas to obtain region-level estimates of water-level rise.