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Wildfires may double erosion across a quarter of western US watersheds by 2050

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Wildfires may double erosion across a quarter of western US watersheds by 2050

Posted: 03 Nov 2015 12:11 PM PST

In recent years, wildfires have burned trees and homes to the ground across many states in the western U.S., but the ground itself has not gotten away unscathed. Wildfires, which are on the rise throughout the west as a result of prolonged drought and climate change, can alter soil properties and make it more vulnerable to erosion. A new study shows that the increase in wildfires may double soil erosion in some western U.S. states by 2050, and all that dirt ends up in streams, clogging creeks and degrading water quality. “It’s a pretty dramatic increase in sediment [entering streams],” write United States Geological Survey (USGS) geologist Joel Sankey and his colleagues, who will speak on the subject on Wednesday, 4 November, at the meeting of the Geological Society of America in Baltimore, Maryland. “The sediment can have a wide range of effects on a lot of watersheds, many of which are headwater streams and important for water supply in the West.” Wildfires whipping across a landscape can burn away ground cover and vegetation, leaving soils exposed and easily erodible by precipitation. In other cases, fires can cause soil surfaces to harden. Instead of gently percolating underground, rain water and melted snow can rush across these hardened surfaces, gaining enough power to erode loose sediments. Sankey and his colleagues wanted to estimate how projected increases in wildfires would change erosion throughout the West between the start of the 21st century and 2050 — the first assessment of fire-induced erosion, said Sankey…. The amount of sediment entering creeks after fires increased with the proportion of the watershed that was burned and if the area burned repeatedly, said Sankey. All that extra dirt can reduce water quality. Soils contain minerals, nutrients and metals, often considered toxic if consumed in large quantities by humans or fish. Large loads of sediment can even dam rivers, changing the course of a creek through its valley. And if the sediment settles in a reservoir, the reservoir will fill with dirt instead of water, severely shortening the lifespan of the water reserve. Restoring forests and improving water quality for human consumption or stream habitat for aquatic animals after a fire is costly, said Sankey, but it may be something water municipalities in the west need to prepare for. In the future, other members of the research team who are co-authors on the study with Sankey will use the erosion results to identify specific communities or watersheds that will be the most prone to fire-induced erosion in the future.

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