Declining snowpacks may cut many nations' water

http://www.eurekalert.org/pub_releases/2015-11/teia-dsm110915.php

Public Release: 12-Nov-2015
Declining snowpacks may cut many nations' water
With warming, possible seasonal deficits from California to Caucasus
The Earth Institute at Columbia University

Gradual melting of winter snow helps feed water to farms, cities and ecosystems across much of the world, but this resource may soon be critically imperiled. In a new study, scientists have identified snow-dependent drainage basins across the northern hemisphere currently serving 2 billion people that run the risk of declining supplies in the coming century. The basins take in large parts of the American West, southern Europe, the Mideast and central Asia. They range from productive U.S. farm land to war-torn regions already in the grip of long-term water shortages.

Snow is an important seasonal water source mainly around large mountain chains. From higher elevations, snowmelt runs gradually into the lowlands during spring and summer growing seasons, when human demand peaks. But global warming is upsetting this convenient balance. Studies show that in many areas, more winter precipitation is falling as rain, not snow, and washing away directly; the snow that does fall is settling at progressively higher elevations, and melting earlier.

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As the world warms, scientists have been observing declining snow accumulations in many regions, a trend that is expected to continue. Once-permanent snowfields are disappearing in the Rocky Mountains from Colorado to northern Montana, as well as in the Himalayas and other areas. A recent study showed that this year the snowpack in California, which is suffering an ongoing drought as well as long-term warming, reached its lowest point in 500 years.

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Also on the list is the volatile Shatt al Arab basin, which channels meltwater from the Zagros Mountains to Iraq, Syria, eastern Turkey, northern Saudi Arabia and eastern Iran. Studies suggest that warming climate has already decreased rainfall and increased evaporation across much of the eastern Mediterranean and Mideast, and a study earlier this year suggested that the spreading civil war now engulfing the region was sparked in part by a record 2006-2010 drought.

The study concentrates only on human water supplies, but lack of snowpack may have wider ecological consequences. In the American West, land managers fear that forest fires undamped by snow might start earlier in the year, and food sources for nesting birds might start running out in late summer. Native trout depend on a steady flow of cold water during summer, so some species could face extinction.

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Yoshihide Wada, a researcher at the Netherlands' Utrecht University who studies global water resources, said the study makes a "convincing argument" that "climate change will add another stressor over many regions" where water scarcity is already an issue. He said this would be especially so in semi-arid areas where irrigation is supplemented by shrinking supplies of groundwater. If anything, the study could underestimate some risks, he suggests, because it does not account for projected increases in population.

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