Global warming over the next century could
significantly reduce the amount of winter snowpack in mountainous areas in the
northern hemisphere, according to a new study published in Nature Climate
Change.
Seasonal snowpack melt is an essential source of fresh
water, and its loss could threaten drinking water supplies, agricultural irrigation
and wildlife ecosystems.
Stanford University climate expert Noah Diffenbaugh
led the study, which compares snowpack conditions across the northern
hemisphere in the late 20th century with climate model projections for the next
one hundred years.
Deceasing
snowpack
Those projections are based on a range of scenarios
which foresee a rise in average global temperatures of between two and four
degrees Celsius.
The study concludes that average snow accumulation
will decrease in most regions of the Western United States, Europe, Central
Asia and the Himalayas, compared to historical patterns.
It projects that low and extremely low snow falls
would exceed the lows of the later 20th century between 10 and 30 percent of
the time with two degrees of warming.
And, Diffenbaugh says, "If the planet warms by
4 degrees Celsius, the United could experience snowpack accumulations below the
levels of the late 20th century up to 80 percent of the years.”
The story is the same in other parts of the northern
hemisphere, where snowpack is a natural, and critical, water reservoir.
Water
worries
The study finds that an early spring melt would
bring more water into the watershed sooner than usual, potentially flooding
rivers, lakes and artificially dammed-river reservoirs.
And with less water available later in the season,
chances for more wildfires, pests, and species extinctions increase.
Diffenbaugh says this timing would also exacerbate
drought conditions when the demand for water is greatest.
“We can infer that should these physical climate
changes occur in the future, that there would be impacts on water supply for
agriculture and for human consumption and for natural ecosystems if the water
storage and management systems are not adapted to those changes.”
According to climate models, extreme rain events are
expected to increase as the planet warms.
However, Diffenbaugh says, that won’t change how the
snowpack responds to climate change.
“Even where there are increases in extreme
precipitation in the models, there are still robust decreases in the amount of
snowpack on the ground at the end of the winter and in robust changes in the
timing of runoff.”
California
experiencing climate extremes
Frank Gehrke takes these findings very seriously. He
heads the California Cooperative Snow Surveys program, which forecasts water
flow from the mountains into man-made reservoirs that provide water for crops
and people.
California is just one part of a broader picture
discussed in the report. Since the state gets little rain in the spring and
summer, Gehrke says timing of snow pack melt is critical.
He says he is seeing greater climate variation than
ever before. “We’re having more extremes in terms of dry and wet years. We see
that not only in our record, but also in discussions with a lot of other people
who are studying climate.”
Gehrke says California water managers need better
measurement tools and higher resolution aerial images of the state’s snowpack
than were available in the Stanford study. For that, the state has turned to
the U.S. space agency’s Airborne Snow Observatory.
Flying at altitudes of about 7,000 meters, the
photo-reconnaissance aircraft capture detailed images of mountain snowpack over
a wide area, allowing scientists to more accurately compute the entire volume
of water in a given watershed.
The NASA flights will also measure how much sun is
reflected from the snowpack, which can indicate how fast it is likely to melt.
Sources :
http://www.voanews.com/content/study-global-warming-threatens-water-supply/1542932.html
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