Asia’s water resource is primarily fed by the Tibetan plate and the mountain ranges in the surrounding area. Many call these ‘water towers’ because of the rivers of glacial and snow melt descending the escalated range. Researchers from the Utrecht University and Future Water have done a study on climate change and the effects that it has had/ will have, on the water towers and in turn, their effect on irrigation and food supply to the lower basins.
The area consists of five major Southeast Asian basins named; Indus, Ganges, Brahmaputra, Yangtze, and Yellow, each with their own unique characteristics. Yangtze has the largest population, but Ganges is the most densely populated. Indus and Brahmaputra have vast amounts of upstream areas and larger glacier areas. And the Yellow and Indus basins are dryer than Ganges, Brahmaputra, and Yangtze. Fig.1 depicts this area which ranges from low (dark green) to high (brown) elevations and blue being elevations 2000 m above sea level. These rivers provide water to more than 1.4 billion people, which is 20% of the world’s population.
Results from an analysis show that the present melt-water plays an important role in the Indus and Brahmaputra river basins. It is most evident in the Indus because the water generated from glacial and snow melt is 151% of the total water naturally caught in downstream areas, whereas the Brahmaputra basin had a percentage of 27%. Meanwhile the contributions to Ganges (10%), Yangtze (8%), and Yellow (8%) are much smaller due to a much limited amount of upstream areas, and more downstream rivers which catch more rainfall.
It is commonly known that glaciers around the world have been reducing in size since the last ice age, and two tests have been done in order to see the differences between a) a best guess of the five major glaciers from today’s date to 2050, and b) an extreme case, in which there are no glaciers. Results show that although there is a decrease from the upper rivers; Indus (-8.4%), Ganges (-17.6%), Brahmaputra (-19.6%), and Yangtze (-5.2%), there was an increase in upstream rainfall; Indus (25%), Ganges (8%), Brahmaputra (25%), Yangtze (5%), and Yellow (14%). Analysis even showed an increase of 9.5% is the Yellow basin because its river is in the downstream and so it barely depends on glacial and snow melt.
It is said that climate change may cause some basins such as Ganges, Indus, and Brahmaputra to become more seasonal, because of the reduced amount of glacial melt, and increase of rainfall. The Yellow basin is expected to become the most, it has been already reported that it shows a consistent increase in accumulation in early spring. Glacial and snow melt caused by climate change will increase in the spring, causing an alleviated drought later in the season.
Regardless of the good effects of rainfall, the Indus and Brahmaputra are expected to reduce considerably in water amounts, due to climate change, causing and accelerated glacier melt and faster river flow. And it shows that this will have an effect on food security. An estimation of 4.5% is expected to be the total population which will be threatened from the reduced water availability.
It is clear then that the Indus and Brahmaputra basins are the most sensitive to food security and downstream water supply. The results of the scenario of a lower amount of downstream water and irrigation were the highest with these two basins. In conclusion, the water towers of Asia are threatened by climate change in the coming years. Although a generalized answer cannot be given because the results differ substantially from basin to basin, there will be an effect. It can be said though, that the Indus and Brahmaputra basins will feel this change the most, mostly because of their high population and density numbers, and their reliance on the river for irrigation and food supply. In the case of the Yellow river, is seems that climate change may have a positive effect. This is because it has a low dependence on glacial and snow melt, and with an increase in upstream precipitation, may even yield positive numbers. If it were retained in reservoirs it would allow for greater water availability, irrigation options, and food supply.
Immerzeel, W.W., van Beek, L.P.H., Bierkens, M.F.P. 2010. Climate change will affect asian water towers. Science, 328 (11 June 2010): 1382-1385.