Northern Hemisphere Snowmelt Shortfalls Could Impact 2 Billion People

Summary: Northern hemisphere snowmelt shortfalls could impact 2 billion people in 97 drainage basins, a study in Nov. 12's Environmental Research Letters finds.

Rio Grande drainage basin in Texas and Mexico has a high risk of snowmelt shortfalls.: Rio Grande Bend near Boquillas Canyon, Big Bend National Park, Texas: Glysiak, CC BY SA 3.0, via Wikimedia Commons

A study published Nov. 12, 2015, in Environmental Research Letters finds that 97 Northern Hemisphere, snowmelt-dependent drainage basins, with a cumulative, current population of about 2 billion people, run a 67 percent risk of declining snow supplies and consequential water shortages from global warming.

The study states succinctly: "Runoff from snowmelt is regarded as a vital water source for people and ecosystems throughout the Northern Hemisphere (NH)."

Out of the study’s selection of 421 Northern Hemisphere drainage basins, 32 register the most likelihood of sensitivity to snow supply fluctuations and have a combined population of about 1.45 billion people. North America’s high-risk basins include Rio Grande, Sacramento and San Joaquin. Other basins especially sensitive to Northern Hemisphere snowmelt shortfalls include the Aegean in the northeastern Mediterranean, Aksu in Central Asia’s Republic of Kazakhstan, Ebro-Duero in northern Spain and Kizil Irmak in Turkey’s Eastern Anatolia region.

Lead author Justin S. Mankin and four co-authors use multi-model and single model ensembles of climate change projections to explore beyond the analytical norm, observed in numerous studies, of evaluating the threat of global warming to the amount and timing of snow accumulation and snowmelt. The study, entitled “The Potential for Snow to Supply Human Water Demand in the Present and Future,” presents the critical factor of the unequal influence of global warming on snow supply and snowmelt runoff in 421 Northern Hemisphere drainage basins.

The study identifies sensitive drainage basins in the snowmelt-dependent Northern Hemisphere where the alternative source of instantaneous rainfall runoff is insufficient to meet human water demands. The 97 basins with projected snowmelt shortages are found to lie near subtropical high pressure centers, within the limited geographical area of about 25 to 45 degrees north latitude. The study’s multi-model also expects 68 drainage basins, with a current, combined population of more than 319 million people, to transition from presently meeting all water demands through rainfall runoff to experiencing water shortages through insufficient rainfall runoff.

Surface and subsurface runoff from rainfall and snowmelt supplement groundwater as sources that supply the human water demand. Snowmelt runoff comprises a critical source for spring and summer water supplies in the Northern Hemisphere.

Internal climate variables complicate the relationship between global warming, snow accumulation and snowmelt. Such snow supply factors as increased freezing elevations, earlier melt runoff and decreased snowfall-to-rainfall ratios drive the magnitude of internal climate variability.

The study finds that about 90 percent of snow-sensitive basins show a span of negative and positive results in the snow resource potential of cumulative spring and summer snowmelt runoff. Three drainage basins in low snow volume baseline climates consistently reveal declines in snow resource potential: the Iberian Peninsula’s Duero-Adour basin in northern Portugal, the Italian Peninsula’s Central Apennines stretching from north to south, and North America’s Rio Grande basin in Texas and Mexico.

The authors note: “Our results emphasize the importance of snow for fulfilling human water demand in many NH [Northern Hemisphere] basins, and highlight the need to account for the full range of internal climate variability in developing robust climate risk management decisions.”

top 32 snow-sensitive basins: Justin Mankin et al./Environmental Research Letters, CC BY 3.0, via IOP Science

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Rio Grande: Glysiak, CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Rio_Grande_in_Big_Bend_NP.jpg

map of top 32 basins: Justin Mankin et al./Environmental Research Letters, CC BY 3.0, via IOP Science @ http://iopscience.iop.org/article/10.1088/1748-9326/10/11/114016

For further information:

"Declining snowpacks may cut many nations' water." EurekAlert > Public Releases. Nov. 12, 2015.
Available @ http://www.eurekalert.org/pub_releases/2015-11/teia-dsm110915.php

Krajick, Kevin, and Kyu Lee. "Declining Snowpacks May Cut Many Nations' Water." The Earth Institute Columbia University > News Archive. Nov. 12, 2015.
Available @ http://www.earthinstitute.columbia.edu/articles/view/3265

Malo, Sebastien. "Declining snowpack, water shortage projected in areas home to 2 billion: study." Reuters India edition > Technology. Nov. 12, 2015.
Available @ http://in.reuters.com/article/2015/11/12/us-usa-climate-water-idINKCN0T10OO20151112

Mankin, Justin S., et al. "The potential for snow to supply human water demand in the present and future." Environmental Research Letters, vol. 10, no. 11 (Nov. 12, 2015). DOI: 10.1088/1748-9326/10/11/114016
Available @ http://iopscience.iop.org/article/10.1088/1748-9326/10/11/114016