Climate Change and Asian Water Towers

Most of Asia’s population is fed with food grown from Himalayan meltwater. 1.4 billion people, over 20% of the world’s population, rely on these mountain water sources. Climate change is predicted to have severe affects on their water and food supply. Until this study, much of the research on climate and precipitation predictions under climate change scenarios has been either local yet anecdotal, or general to the continent without specificity to regional variations. This study aimed to identify the main river runoff<!–[if supportFields]> XE “runoff” <![endif]–><!–[if supportFields]><![endif]–> areas fed by Himalayan water, and predict the effects of climate change on water availability in those areas, considering regional differences. The main components of river basins which will be altered by climate change are the importance of meltwater on downstream hydrology, the changing ice-covered landscapes (glaciers<!–[if supportFields]> XE “glaciers” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “glacier” <![endif]–><!–[if supportFields]><![endif]–>), and the water supply from upstream basins which dictate food security. The authors focused on the Indus, Ganges, Brahmaputra<!–[if supportFields]> XE “Brahmaputra” <![endif]–><!–[if supportFields]><![endif]–>, Yangtze, and Yellow river<!–[if supportFields]> XE “Yellow river” <![endif]–><!–[if supportFields]><![endif]–> basins and food growing areas. The predicted effects of climate change will be quite different on each of these areas, according to the results.—Asa Smith Kamer
Immerzeel, W., Van Beek, L., Bierkens, M., 2010. Climate Change Will Affect the Asian Water Towers. Science 328, 1382–1385

Each region features many different types of glacier<!–[if supportFields]> XE “glacier” <![endif]–><!–[if supportFields]><![endif]–> which each respond differently to climate changes. Immerzeel et al. aimed to use hydrology models which would not be affected by reservoirs or downstream extraction which can calculate the discharge into whole basins, rather than from only one type of glaciers<!–[if supportFields]> XE “glaciers” <![endif]–><!–[if supportFields]><![endif]–>. These models found that reduced meltwater would have the most significant effect on the Brahmaputra<!–[if supportFields]> XE “Brahmaputra” <![endif]–><!–[if supportFields]><![endif]–> and Indus river<!–[if supportFields]> XE “Indus river” <![endif]–><!–[if supportFields]><![endif]–> basins. Of the examined basins, these two rely most heavily on snow and glacier water. The other three, the Yangtzee, Ganges, and Yellow river<!–[if supportFields]> XE “Yellow river” <![endif]–><!–[if supportFields]><![endif]–> valleys, each have less flow from meltwater for various reasons: relatively larger catchment areas, smaller glaciers, more of a reliance on water from monsoon<!–[if supportFields]> XE “monsoon” <![endif]–><!–[if supportFields]><![endif]–> precipitation. In the Brahmaputra and Indus river valley 40% of downstream water is meltwater, whereas in the other river valleys the contribution of glacial melt is much less significant.
Each of these regions uses upstream dams and reservoirs in order to regulate water availability for agriculture<!–[if supportFields]> XE “agriculture” <![endif]–><!–[if supportFields]><![endif]–>. Any changes of water flow into these holding systems will have significant effects on the downstream populations that rely on local food sources. The data found that although smaller glaciers<!–[if supportFields]> XE “glaciers” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “glacier” <![endif]–><!–[if supportFields]><![endif]–> will mean less available water in all of the 5 river regions, the decrease of meltwater will be somewhat, though not totally, mitigated by increased upstream rainfall which is predicted in climate change scenarios. In the case of the Yellow river<!–[if supportFields]> XE “Yellow river” <![endif]–><!–[if supportFields]><![endif]–>, river flow is actually predicted to increase. The authors also mentioned though, that these cumulative results should be treated with skepticism because the current climatology and precipitation modelling techniques are unrefined and so far unproven. Regardless of these uncertainties the Brahmaputra<!–[if supportFields]> XE “Brahmaputra” <![endif]–><!–[if supportFields]><![endif]–> and Indus river<!–[if supportFields]> XE “Indus river” <![endif]–><!–[if supportFields]><![endif]–> valleys show the most vulnerability with predicted consistent decrease of water availability.
The authors connected the predicted future water amounts with measures of food production potential such as water available for irrigation, crop yields, caloric value of crops, and the amount of energy people require from their diets. With these data they were able to predict how many fewer people would be able to be supported in each region as agricultural water supply decreases. They found that compared to current trends predicted future food production will decrease significantly (most significantly in the Brahmaputra<!–[if supportFields]> XE “Brahmaputra” <![endif]–><!–[if supportFields]><![endif]–> and Indus areas because of high populations and strong reliance on meltwater for irrigation).
The authors found in this study that the Himalayan glaciers<!–[if supportFields]> XE “glaciers” <![endif]–><!–[if supportFields]><![endif]–><!–[if supportFields]> XE “glacier” <![endif]–><!–[if supportFields]><![endif]–>, Asia’s “Water Towers”, are sensitive to climate change, and that their melting will have significant effects on downstream human populations. They also found however, that these changes will vary greatly by region, and may not be as severe as previous research has suggested.

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