for National Geographic News
Is spring coming earlier these days?
Maybeat least in places where "spring" can be defined as the time when snowmelt floods the rivers, according to a new U.S. Geological Survey study published March 21 in the journal Geophysical Research Letters.
Hydrologist Glenn Hodgkins and a colleague at USGS's Maine Water Science Center examined stream-flow records from 179 rural rivers in the northeastern U.S. and southeastern Canada.
The records are maintained via gauging stations, which measure stream flow by tracking water depth.
Only rivers that had been monitored for at least 50 years were used, and only relatively small ones (the average stream flows of larger rivers are more likely to have been artificially affected by the construction of dams). Some streams had been monitored for as long as 90 years.
In a prior study of New England rivers, Hodgkins had found that total annual flow had not significantly changed. In his recent study, he found that in many of the rivers north of 44° north latitude (where winter snow plays the biggest role) the time of peak runoff had shifted earlier by about five to ten days over the last 50 years.
Hodgkins's finding comes hard on the heels of a 2005 study that found similar results in western North America, where mountain snow feeds many rivers.
"We investigated 300 snowmelt-dominated rivers from California to Alaska," said Iris Stewart-Frey, who led the study for the Scripps Institution of Oceanography in La Jolla, California.
"We found that snowmelt is coming earlier over the past few decades."
What Difference Does It Make?
The implications are a bit different in the East and the West.
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