If there’s one hurdle that the proposed Ganga project will not run into, it will be water supply. Not till 2050, at least. And there’s going to be an abundance of it. The reasons, however, should be disconcerting — this will be on account of climate change.
A projected increase in precipitation and glacier melt due to climate change, in fact, will result in greater runoff from rivers in High Asia until at least 2050, a paper published online in Nature Climate Change has projected. This suggests that discussion of water availability in this region must also include seasonal changes and extreme weather events.
Arthur Lutz of Utrecht University and colleagues used a high-resolution model to quantify the hydrology of five major river basins — Indus, Ganga, Brahmaputra, Salween and Mekong — in the High Asia region. Different rivers have different runoff composition: for example, the upper Indus Basin is dominated by glacier melt, which makes up 40.6 per cent of the streamflow, compared with the upper Mekong Basin, where glacier melt makes a minimal contribution. The team used climate model outputs to investigate how climate change will impact water availability up to 2050.
For the Ganga, Brahmaputra, Salween and Mekong river basins, glacier melt is not expected to change, as the effects of decreased glacier area will be compensated by increased melt rates. Rainfall is projected to increase due to climate change by up to 9.5 per cent for these four basins. For the fifth, the upper Indus Basin, which is melt-dominated, the researchers expect accelerated melt, although rainfall is projected to slightly decrease.
The researchers wrote, “Despite its larger relative glacierised area, glacier melt contributes only 11.5 per cent of the total runoff generated in the upper Ganga Basin (UGB). Owing to the monsoon-dominated precipitation regime in the UGB, the runoff regime is rain dominated here. The hydrological regime in the upper Brahmaputra Basin (UBB) is comparable to the UGB, although the relative contribution of glacier melt and snow melt in the UBB is slightly larger compared with the UGB.”
They observed, “For all basins, the amount of glacier melt water contributing to the total flow does not change much at least until 2050 because the decrease in glacier area is compensated by an increase in melt rate.”
For the rainfall-runoff-dominated UGB, the future hydrology largely depends on the precipitation projections. These projections have very large uncertainties, and large variation between the annually averaged and seasonal projections.
Lutz and others said, “The absolute amounts of glacier-melt and snow-melt donot change much, but their relative contributions decrease owing to the increased rainfall runoff. As a consequence, increased flows are observed during the discharge peak in the monsoon season, with large uncertainty in the magnitude of flow increase.”
The study was a collaborative effort of FutureWater, Utrecht University and the International Centre for Integrated Mountain Development (ICIMOD). The findings are part of a larger research programme titled Himalayan Climate Change Adaptation Programme.
