From: Andy Soos, ENN
Published June 21, 2010 05:27 PM

Asian Rivers Impacted by Clmate Change

It all depends on where you are. When weather patterns change rainfall will increase some places and decrease in other places. What has the most impact is those river systems that many people depend on. Two of Asia's major rivers are the the Brahmaputra and Indus river basins that descend from the Himalayas into India. According to some recent study these two are likely to be severely affected by climate change while others will be less affected and could even benefit.

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One-fifth of the world's population is dependent on water from the Brahmaputra, Indus, Ganges, Yangtze and Yellow rivers which are fed by melt water from the Himalayas. Initially it was thought that all the Asian river basins would be similarly impacted by climate change, which would both reduce the amount of water available and harm food security from a reduction in water supplied from glacial reserves. Indeed there has been recent controversy about the extent of glacial melt in this area.

Netherlands scientists has recently used computer simulations to assess the effects of climate change.

"We started to look into this problem because we were observing discussions about the importance of glacial melt from the Himalayas for 1.5 billion people, without seeing any hydrological assessments of the actual contribution of melt water to water availability," said Mark Bierkens, chair of the department of physical geography at Utrecht University, and one of the study authors.

Their simulation shows that climate change will hasten the melting of upstream snow and ice reserves, leading to faster and heavier water flow and flooding downstream  although the exact rate and extent of the impact is still unclear. They also predicted that climate change would dry up some major rivers because of higher evaporation of water.

Overall their report studied the current importance of meltwater, observed cryospheric (glacial reserves) changes, and the effects of climate change on the water supply from the upstream basins.

Some of the results showed that meltwater plays an important role in the Indus and Brahmaputra river basins. This is most evident in the Indus: Discharge generated by snow and glacial melt is 151% of the total discharge naturally generated in the downstream areas. In the Brahmaputra basin this amounts to 27%. The contribution of snow and glacier water to the Ganges (10%), Yangtze (8%), and Yellow (8%) rivers is limited owing to comparatively large downstream areas, limited upstream precipitation, smaller glaciers, and/or wet monsoon dominated downstream climates

So a loss of glacial reserves may affect the Indian river basins more so than the Chinese river basins.

The effects on the Indus and Brahmaputra basins are likely to be severe due to dwindling glacial reserves owing to the large numbers of people living in the area and their heavy dependence on irrigated agriculture.

Alternately people in the Yellow River basin, China, could benefit, as they depend less on irrigation, and also because the projected higher rains upstream could be retained in reservoirs for use later for crops.

"It turns out that downstream water availability is most dependent on upstream melt water for the Indus, moderately important for the Brahmaputra and less important for the other rivers (where water availability depends on downstream monsoon rainfall)," stated Bierkens, whose work was published in Science.

Climate and river effect predictions are difficult and unpredictable but the current research suggests a certain type or priority in future river water usage.

For further information: http://www.sciencemag.org/cgi/content/full/328/5984/1382?ijkey=bJbIXcdg/F42Y&keytype=ref&siteid=sci

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