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South Asia river water flow seen increasing on global warming

New Delhi : A wetter future awaits South Asia. A new study based on global climate change models that informed the fifth assessment report of the UN’s Intergovernmental Panel on Climate Change has indicated that the South Asia region will see a 20–30 per cent increase in mean annual runoff for the period 2046–2075 relative to the study baseline period of 1976–2005.

Water security in South Asia will be under increasing stress owing to socio-economic growth and global climate change. It is forecasted that the population in South Asia will be more than 2.3 billion by 2050.

The growth of population and expanding economies will result in an increase in water demand. Meanwhile, there is strong evidence that many parts of South Asia are experiencing long-term warming trends that will continue into the future. The changes in climate will have significant impacts on water availability. Moreover, the warmer future climate will increase evapotranspiration and hence increase demand for water in irrigated agriculture, urban centres and water-dependent ecosystems.

South Asia is home to as many as 54 rivers of varying sizes linked to the Indus, Ganga and Brahmaputra river basins, all originating in China’s Tibet Autonomous Region.

While the Indus basin connects China with Afghanistan, India and Pakistan, the Brahmaputra and Ganga basins connect Bangladesh, Bhutan, China, India and Nepal.

The study was recently published in the Journal of Hydrology: Regional Studies and was carried out by the Australia-based Commonwealth Scientific and Industrial Research Organisation.

"The modelling results indicate that future runoff will increase throughout most of the region except in the far north-east and far north-west. The median projection shows increases in mean annual runoff of 20–30 per cent in the Indian sub-continent for 2046–2075 relative to 1976–2005. The change in runoff is driven mainly by the change in precipitation, moderated (in wetter futures) or intensified (in drier futures) by higher temperature and potential evaporation", the study said.

Hongxing Zheng, corresponding author of the study, was quoted as saying to SciDev.Net that it was also discovered that the percentage change in precipitation may amplify by 1.5–2 per cent in wet areas and by more than two per cent in dry areas.

“A spike in mean annual runoff of about 10 per cent is projected for the Indus, Tibetan Plateau and Arakan Coast regions, and about 15 per cent in the Ganga-Brahmaputra, Deccan Plateau and Ghats Coast regions,” Hongxing said, adding that the spike will be over 20 per cent in the Narmada-Tapti region and Sri Lanka.

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