According to an article by three Utrecht University researchers published in the journal Science on 11 June, climate change will drastically reduce the discharge of snow and ice meltwater in a region of the Himalayas, threatening the food security of more than 60 million people in Asia in the coming decades. The Indus and Brahmaputra basins are expected to be the most adversely affected, while in the Yellow River basin the availability of irrigation water will actually increase.
More than one billion people depend on the meltwater supplied by the Indus, Ganges, Brahmaputra, Yangtze and Yellow River. The snow and ice reserves situated upstream are important in sustaining the availability of water downstream. Researchers from Utrecht University and FutureWater have calculated the reduction in glacier and snow coverage and forecasted the future river discharge and made predictions about food security in the basins of these five major rivers.
How important is meltwater?
“The role of meltwater in the Indus basin is much more significant than that in other river basins in Asia,” according to Walter Immerzeel, hydrologist at Utrecht University and FutureWater.
“The downstream sections of the Indus are dry, are home to one of the largest irrigation networks in the world and are completely dependent on meltwater.”
Taken while facing south on the Tibetan plateau near Tingri, close to the Mount Everest base camp, at an elevation of 4380m above sea level, this photo illustrates the ‘water tower’ function of the Himalayas.
Photo credit: A. Hamer
Climate change will ultimately result in declining discharge levels of the major Asian rivers, impacting the volume of irrigation water available. “Our model calculations show that the Brahmaputra and Indus are the most vulnerable. According to our estimates, this will threaten the food security of the approximately 60 million inhabitants of these areas by the year 2050,” explains Immerzeel. “However, the opposite is also possible. In the Yellow River basin, an increase in wintertime rainfall is expected, resulting in increased availability of water early in the growing season.”
Taken while facing south on the Tibetan plateau near Nagarze, close to Yamdrok Lake, at an elevation of 4463m above sea level, this photo illustrates the ‘water tower’ function of the Himalayas.
Photo credit: H. Helleman
Uncertainty about glaciers
The size and discharge of Himalayan glaciers are experiencing significant decline due to climate change. “However, observed glacial decline varies greatly from region to region, and there is a high degree of uncertainty regarding the speed of decline,” says Marc Bierkens, hydrology professor at Utrecht University. “However, the trends identified in the river discharge forecast do not take this uncertainty into account.” The researchers based their results on a combination of hydrologic models, climate forecasts from five different climate scenarios, and satellite images depicting snow and ice, rainfall, and changes in the Earth’s gravitational field.
This study was financed in part by the Netherlands Organisation for Scientific Research (NWO).
Paper in Science
Walter Immerzeel, Rens van Beek, Marc Bierkens (all associated with Utrecht University), ‘Climate change will affect the Asian water towers’, Science, 11 June 2010.