09d

• Board Meeting Date: 3/18/2008
• Description: CWCB Director's Report
• Board Meetings - Doc Type: Memo

In Colorado, colder temperatures will protect the snowpack -and reservoirs are large enough to store
several years of water supply.
But in California, reservoirs already operate on a delicate balance.
They are kept well below capacity during the winter as protection against flooding. After the rainy season,
they are filled with the spring snowmelt, storing water to be released during the dry sumrner months.
Heavier winter rains and earlier snowmelt probably will overwhelm reservoirs, forcing an early release of
water. That would leave too little water for the summer.
Between 1950 and 1999, the period the researchers examined, the total amount of precipitation that fell in
the Rockies, the Cascades, the Sierra Nevada and smaller mountain ranges across the West did not vary
significantly.
But the portion arriving as snow steadily declined, falling by an average of 4.3 percent per decade in the
nine areas included in the study.
Average daily minimum temperatures between January and March climbed an average of 0.34 degrees
Celsius per decade.
And three rivers -the Columbia, Sacramento and Colorado -ran higher earlier in the year.
DECLINE IN SNOWPACK FLAMED ON WARNIING -The persistent and dramatic decline in
the snowpack of many mountains in the West is caused primarily by human-induced global warming and
is not the result of natural variability in weather patterns, researchers reported yesterday.
Using data collected over the past 50 years, the scientists confirmed that the mountains are getting more
rain and less snow, that the snowpack is breaking up faster and that more rivers are running dry by
summer.
The study, published online yesterday by the journal Science, looked at possible causes of the changes --
including natural variability in temperatures and precipitation, volcanic activity around the globe and
climate change driven by the release of greenhouse gases. The researchers' computer models showed that
climate change is clearly the explanation that best fits the data.
Many in the West and the Southwest depend on the snowpack's springtime melt for power, irrigation and
drinking water. When the snow fields melt earlier and more suddenly, dams are able to capture less of the
water and must release more of it to flow on to the ocean.
Although parts of the West have been hit by record snowfalls this winter, the data collected by the team
showed that since 1950, the water content of the snowpack as of April 1 each year has decreased in eight
of the nine mountain regions studied, by amounts ranging from 10 percent in the Colorado Rockies to 40
percent in the Oregon Cascades. Only the southern Sierra Nevada range did not show a drop.
The study is part of what has become a drumbeat of dire assessments based on reports of quickening
climate change caused by the buildup of carbon dioxide from vehicles, power plants, industry and
deforestation. Last week, the American Geophysical Union, a leading scientific group in the field, issued
a warning that "Earth's climate is now clearly out of balance and is warming."
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