Photo: Anja Disseldorp/Flickr
It's conventional climate-change wisdom at this point that as the planet warms, the glaciers of the Himalayas, which every spring feed water into rivers that supply some of the most densely-populated areas of South Asia, will retreat. This will, at first, increase the water supply, before then decreasing it. The reasoning remains sound, but some new research gets a bit more detailed on the connection between glacier melt and water availability over the next century. For now, the news actually isn't so bad.
Pakistan's The Dawn newspaper reports that scientists from Utrecht University have run climate simulations to try and precisely determine what effect glacier melting will have on the watersheds that feed the Indus River–running through the most populated area of Pakistan–and the Ganges River, which runs through one of the most densely populated parts of India and into Bangladesh.
By 2100 under high emissions scenarios (where we're headed…), the scientists say the glaciers in both watersheds will have lost about half their current volume. However, at least this century, this will not affect overall water availability in the areas that depend on these rivers.
The reason? Rising runoff from the glaciers will likely be able to keep up with rising demand for water, as population and water use grows. Though 2050 the amount of glacial runoff is set to keep rising.
Once glacial runoff peaks, and eventually declines to lower levels than today, the rivers in the region will have to rely on the monsoon—which already is responsible for about 70 percent of their flow—for the majority of their water supply.
When South Asia's major rivers become fed largely or exclusively by monsoon rains—which, again, these scientists say is something that likely won't happen this century—things could get rough for the region.
The effect of climate change on the monsoon in South Asia is difficult to predict, with different studies showing multiple possible scenarios.
In the perhaps worst case, abrupt climate change could drag the monsoon out over the sea, dumping its rain there rather than over land. In other scenarios the monsoon could have more rain, but it could fall in more intense bursts making it more difficult to manage the flow—a graphic example of this sort of precipitation being the recent flooding in the Indian state of Uttarakhand, which washed away villages and killed thousands. Other reports show how the monsoon could be delayed and decrease in intensity. Which is all to say, there's a lot of variability here, but none of the scenarios show things staying as they are now.