Deforestation in snowy regions causes more floods

Environmental Research Web via the American Geophysical Union: New research suggests that cutting down swaths of forest in snowy regions at least doubles – and potentially quadruples – the number of large floods that occur along the rivers and streams passing through those forests.

For decades, the common perception in hydrology has been that deforestation in such areas made seasonal floods bigger on average, but had little effect on the number of large floods over time, said geoscientist Kim Green of the University of British Columbia. But a new study by Green and her co-author Younes Alila published today in Water Resources Research, a journal of the American Geophysical Union, suggests that deforestation consistently causes more floods – both big and small.

In the interior regions of North America, many creeks and rivers get most of their flow from melting snow accumulated during winter storms in mountainous areas. How much water flows down these streams depends not only on how much snow falls upstream, but how fast the snow melts. But deforestation shines a new – and glaring – light on this water source. While ordinarily the trees keep the melting under control by shielding snow from the sunlight, "as soon as you get rid of the trees, the snow melts faster," said Green. "It's that simple."

The difference between Green and Alila's study and what hydrologists have historically done is how they crunched the data. In the past, hydrologists used a technique called chronological pairing – they compared each year's flood data from a stream in a deforested area to that year's data from a nearby, fully forested stream. This allowed the scientists to describe how floods become larger on average in deforested areas....

A snowy forest in Boreal, California, shot by Brocken Inaglory, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license