Black Snow Causes Early Runoff January 13, 2009
Soot from pollution causes winter snowpacks to warm, shrink and warm, which sends snowmelt streaming down mountains as much as a month early, a new Dept. of Energy study finds. How pollution affects a mountain range's natural water reservoirs is important for water resource managers in the western U.S. and Canada who plan for hydroelectricity generation, fisheries and farming.
Scientists at the DOE’s Pacific Northwest National Laboratory conducted the first-ever study of soot on snow in the western states at a scale that predicted impacts along mountain ranges. They found that soot warms up the snow and the air above it by up to 1.2 degrees F, causing snow to melt. "If we can project the future -- how much water we'll be getting from the rivers and when -- then we can better plan for its many uses," said PNL scientist Yun Qian. "Snowmelt can be up to 75% of the water supply, in some regions. These changes can affect the water supply, as well as aggravate winter flooding and summer droughts."
This study revealed regional changes to the snowpack caused by soot, whereas other studies looked at the uniform changes brought by higher air temperatures due to greenhouse gases. Qian used a climate computer model to zoom in on the Rocky Mountain, Cascade, and other western U.S. mountain ranges. He found that changes to snow's brightness results in its melting weeks earlier in spring than with pristine snow. In addition, less mountain snow going into late-spring means reduced runoff in late-spring and summer. They will report their findings in an upcoming issue of the Journal of Geophysical Research -- Atmospheres. "Earlier studies didn't talk about snowpack changes due to soot for two reasons," said co-author William Gustafson. "Soot hasn't been widely measured in snowpack, and it's hard to accurately simulate snowpack in global models. The Cascades have lost 60% of their snowpack since the 1950s, most of that due to rising temperatures. We wanted to see if we could quantify the impact of soot."
Source: Pacific Northwest National Laboratory
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