Rivers Indicate Earlier Snowmelt in Eastern North America
AEN News
Washington - Scientists at the U.S. Geological Survey (USGS) have
found evidence in eastern North America that the snow is melting
and running off into rivers earlier than it did in the first
half of the 20th century. According to a USGS study published
in the most recent issue of Geophysical Research Letters,
winter-spring flows in many rivers in the northern United
States and Canada are occurring earlier by 5-10 days.
"We studied rural, unregulated rivers with more than 50 years
of USGS and Environment Canada river flow data," explained
Glenn Hodgkins, lead author and hydrologist at the USGS Maine
Water Science Center. "Some 179 rivers in eastern North
America met the criteria of our study with 147 in the United
States from the Dakotas to New England and 32 in Canada from
Manitoba to Newfoundland. These rivers are sensitive to
changes in precipitation and temperature," added Robert
Dudley, study co-author.
The scientists compared the dates by which half of the total
volume of winter-spring runoff has flowed past a river
gaging station in each year. Most rivers north of 44°
north latitude--roughly from southern Minnesota and
Michigan through northern New York and southern Maine--showed
earlier winter-spring streamflows. In contrast, many
stations south of this line in Iowa, southern Wisconsin,
and northern Illinois had later streamflows. Changes
in average monthly flows support these results--there
are high percentages of rivers north of 44° north
latitude with increases in January, February, and
March streamflows and relatively high percentages
of rivers with decreases in May and June.
In 2005, researchers from Scripps Institution of Oceanography
and the USGS found earlier streamflow across large portions
of western North America in rivers with significant snowmelt
runoff.
The documented changes in the timing of winter-spring streamflows
in eastern North America may be important to aquatic ecosystems
but the impacts of these changes are not well understood. One
possible impact may be on the survival rate of Atlantic salmon.
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