By Mason Inman
This post is part of a special National Geographic News series on global water issues.
Some of Asia’s mighty rivers will be hit hard by climate change, with nearly 60 million people facing potential food shortages as a result, but other rivers will see little change, as was previously predicted, according to a new study this month in the journal Science.
However, two other major rivers–the Indus, which feeds Pakistan, and the Brahmaputra, which runs through eastern India and Bangladesh–could lose large amounts of water, resulting in a huge rise in hunger.
Asia’s “water tower’–the snow and glaciers in the Himalayas and Tibetan plateau–supplies some of the world’s largest rivers. In turn, these rivers support nearly 1.5 billion people, or one-fifth of the world’s population. Some previous reports argued that most of these rivers would be hit hard as temperatures rise, forcing river flows to dwindle to a trickle.
One such claim–a major report of the Intergovernmental Panel on Climate Change published in 2007–was retracted (pdf) earlier this year as a mistake.
In the new study, lead researcher and Utrecht University hydrologist Walter Immerzeel said, “We project significant decreases in discharge–but the rivers won’t run dry.”
The new study used climate models to estimate what would happen by mid-century if greenhouse gas emissions continued to rise under “a business-as-usual scenario,” climbing to about double current yearly emissions.
The meltwater from the snowpack and glaciers “plays only a modest role for the Ganges, Yangtze, and Yellow rivers,” the study said, explaining that these river basins depend more on rainwater than glacial melt. However, it “it extremely important in the Indus basin and important for the Brahmaputra basin.”
With today’s often inefficient agricultural systems, the drop in water by mid-century would mean that Pakistan, eastern India, and crowded Bangladesh would struggle to feed growing populations.
The Indus would be capable of supporting about 25 million fewer people, the study estimates. In the Bramaputra basin, the drop in flows would mean river-based irrigation could support just 27 million people–less than half the current population.
So, the researchers argue, these hard-hit areas would likely need to revamp their agricultural methods to use water more efficiently.
They might need “different crop varieties which are less water-consuming,” said Immerzeel, or they could adapt by “providing economic incentives to farmers to use less water.
For more on Asia’s water tower:
National Geographic magazine: Tibetan Plateau
National Geographic News: “Goddess” Glacier Melting in War-Torn Kashmir
National Geographic News: “Venice of Asia” Canals Disappearing
For more on water and how to conserve, visit National Geographic’s freshwater website.
Photograph of Gangotri Glacier, India by George F. Mobley, National Geographic
This post has been edited from its original form.