Ganga, Brahmaputra, Indus water levels to rise by 2050: IPCC report

The runoff in the Indus, Ganga and Brahmaputra rivers is expected to increase due to accelerated snowmelt from an increased precipitation, says the IPCC’s Sixth Assessment (AR6) report. The basins of these rivers, which provide water to the most densely populated areas of south Asia, will see an increase in the ‘runoff’ of between 3 to 27 percent by the mid-century, according to report on Impacts, Adaptation and Vulnerability, released February 27, 2022. ‘River run-off’ refers to water that comes into a river water system from sources such as rainfall, melting snow and groundwater.

The IPCC projects a 7-12 percent of runoff in the Indus, 10-27 percent in the Ganga and 3-8 percent in the Brahmaputra. The increase in run-off in the upper Ganga and Brahmaputra would be due to a rise in precipitation, while in the Indus, it would be due to accelerated melting snow. The future hydrological extremes of the Upper Indus, Ganges and Brahmaputra river basins suggest an increase in the magnitude of extremes towards the end of the 21st century, mainly due to increase in precipitation extremes. The intensity and frequency of extreme discharges is also likely to increase towards the end of the century. The intensity and frequency of extreme discharges is also likely to increase towards the end of the century.

The future of the upper Indus basin water availability is highly uncertain in the long run due to uncertainty surrounding precipitation projections. The run-off in the Brahmaputra, Ganga and Meghna is projected to increase by 16 percent, 33 percent and 40 percent respectively under the climate change scenarios by the end of the century. The changes in run-off in these scenarios are larger in the wet seasons than the dry season. Extreme precipitation events are also expected to increase to a higher degree in the Indus than the Ganga and Brahmaputra basins, according to the report.

“Increase in extreme precipitation events is likely to cause more flash flood events in the future. In case of Indus, increasing temperature trend in the future may lead to accelerated snow and ice melting which may increase the frequency and intensity of floods in the downstream areas,” said the report. The Ganga-Brahmaputra region also faces the threat of increased frequency of flood events. The Ganga basin also shows a higher sensitivity to changes in temperature and precipitation. Worryingly, future flow would increase in the Central Himalayan region in Nepal, which would have ‘serious consequences downstream’, the report said.