U Wash Study - Warmer Climate Means 20% Loss Of Winter Snowpack In Cascade Mountains - PI

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SPOKANE, Wash. -- Climate change appears to be cutting the winter snowpack in Washington's Cascade Range by at least 20 percent, according to a researcher at the University of Washington. Rising temperatures mean more of the snow falls with a high water content, and melts and washes away long before it is needed by users in spring and summer months, the research found.

"All things being equal, if you make it one degree Celsius warmer, then 20 percent of the snowpack goes away for the central Puget Sound basin, the area we looked at," said Joseph Casola, a UW doctoral student in atmospheric sciences.

His research looked at records from the annual April 1 measurement of the winter snowpack, and then used different methods to try and estimate how water content might have changed as a result of climate change. Average temperatures in Washington rose about 1.5 degrees during the past century, according to the UW's Climate Impacts Group. That meant more winter precipitation fell as rain or melted more quickly.

Ideally, snow that falls in the winter melts slowly in the spring and summer months, filling reservoirs in the Cascades. The water is released gradually to supply drinking water, water for fisheries and hydropower and irrigation water for farms. Precipitation that falls as rain or as snow with a high water content tends to wash down rivers or into the ground during winter months, when it is not needed.

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http://www.seattlepi.com/local/6420ap_wa_snowpack_climate.html

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1. 1C.

[OKIsItJustMe]

2. Any way you slice it, warming climate is affecting Cascades snowpack

http://uwnews.org/article.asp?articleID=49664

May 12, 2009 | Science | Environment

Any way you slice it, warming climate is affecting Cascades snowpack

Vince Stricherz [e-mail]
Stephanie Kenitzer [e-mail]

There has been sharp disagreement in recent years about how much, or even whether, winter snowpack has declined in the Cascade Mountains of Washington and Oregon during the last half-century.

But new research leaves little doubt that a warmer climate has a significant effect on the snowpack, as measured by water content on April 1, even if other factors keep year-to-year measurements close to normal for a period of years.

Water content can vary greatly depending on temperature and other conditions at the time of snowfall. Typically an inch of snow at temperatures near freezing will contain significantly more water than an inch of snow a colder temperatures.

"All things being equal, if you make it 1 degree Celsius warmer, then 20 percent of the snowpack goes away for the central Puget Sound basin, the area we looked at," said Joseph Casola, a University of Washington doctoral student in atmospheric sciences.

That means that even in years with normal or above-normal snowfall, the snowfall probably would have been even greater except for climate warming. The finding has implications for various water-dependent resources, including drinking water supplies, fisheries, irrigation and hydropower, and it could be applicable to other areas of the Cascades in the Pacific Northwest.

Annual snowfall variability makes it difficult to plot a meaningful trend, Casola said. Starting in a year with high snow accumulation will imply a significant decrease over time, while starting in a year with average or low snow totals will imply little change or even an increase. So, for example, measuring from 1944 to 2005 shows just a slight decline in snowpack but changing the starting year to 1950 more than triples the decline.

However, the measurements also show a slight increase in the last 30 years, a period of significant climate warming. That is probably because trend measurements include declines from climate warming as well as increases and decreases from other factors. For example, several of the lowest-snow winters in the Puget Sound area were during El Niño years, while many of the highest-snow winters were during La Niña years. Those two climate phenomena in the South Pacific can have significant impact on Northwest weather. Likewise, the amount of snow can be affected by a long-term climate cycle in the North Pacific called the Pacific Decadal Oscillation, which changes between positive and negative phases on the order of every 20 years.

"Global warming can be reducing your snowpack over time, but other factors can mask the impact of the warming," Casola said. "Conversely, in a period of dry years global warming would tend to exacerbate the effects."

The new research used four different methods to examine decades-long records of water contained in Cascades snowpack in the central Puget Sound basin on April 1 of each year. Scientists used simple geometry to estimate temperature sensitivity of snowpack, made detailed analysis of seasonal snowpack and temperature data, used a hydrological model to examine the data, and analyzed daily temperature and precipitation measurements to estimate water content of snowpack on April 1.

"If you assume precipitation is the same every year and look at the effects of temperature alone, all the ways we examined the data converge at about a 20 percent decline in snowpack for each degree Celsius of temperature increase," said Casola.

He is lead author of a paper detailing the work, part of his doctoral thesis, which is being published online May 14 in Journal of Climate, published by the American Meteorological Society. Co-authors, all from the UW, are Lan Cuo, Ben Livneh, Dennis Lettenmaier, Mark Stoelinga, Philip Mote and John M. Wallace.

While there still is uncertainty in the trend data, people can expect to see lower spring snowpack more frequently in the future, with low-snow winters bringing low-flow summers, Casola said. Winter precipitation in the Cascades is likely to be similar to what is recorded now, but more of it will be rain.

Casola notes that businesses, resource manager, utilities and irrigators increasingly accept the notion of climate change, and many try to incorporate the information into long-term plans.

"Now they want to know, 'What does this mean for my operation?'" he said. "People are becoming more savvy to the issue of climate change. They want to be aware of changes that might be coming and to identify areas in their systems that perhaps need to be modified."

The work was funded by the National Science Foundation and the Joint Institute for the Study of the Atmosphere and Ocean at the UW.

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For more information, contact Casola at 206-543-5754 or [e-mail].

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3. Does this mean we might see 60 degrees

sometime this summer? I was hoping to have a chance to run my down vest and parka through the laundry before the rainy season sets in again. Not that it has actually stopped, but today it was kind of a dry rain, so it might be going to quit doing what it's been doing and do something else. Maybe something a little bit warmer.