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Large wildfires bring increases in annual river flow

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Staff Writer | April 16, 2018
Large wildfires cause increases in stream flow that can last for years or even decades, according to a new analysis of 30 years of data from across the continental United States.
annual river flow
Nature   The bad news is more water can also be a detriment
Enhanced river flows are a good news, bad news proposition. The good news is more water can be a boon, such as serving as a hedge during times of scarce water.

The bad news is more water can also be a detriment, especially when it comes with an increase in contaminants, such as sediment or nutrients, caused by the greater runoff that follows vegetation losses to fire.

Prescribed burns on the other hand were not found to significantly alter river flows.

“That suggests smaller, prescribed burns can be a management tool for potentially decreasing the threat of bigger fires and creating more resilient forests without having a major effect on water yields,” said co-corresponding author Kevin Bladon of Oregon State University.

The findings are important because they bring new insights into how water resource managers should look at fire, especially with the frequency of severe blazes on the rise in the face of global climate change.

Bladon, a hydrologist in OSU’s College of Forestry, and collaborators looked at three decades of data regarding fires, climate and river flow from 168 river basins in the lower 48 states.

In watersheds where more than 19 percent of the forest burned, annual river flow increased significantly.

“The impacts of big fires on surface freshwater resources hadn’t been previously studied at this scale, nor have they been factored into regional water management strategies,” Bladon said.

“But large fires are increasing and that heightens concern about their impacts on water in our forest streams and for downstream potable water.”

More than two-thirds of U.S. municipalities get their drinking water from a source that originates in a forest, he said.

“Trace the water back from that tap in your kitchen and you begin to see why it’s important to care about what can happen when there’s a large fire in the forest where your water comes from,” he said.

“And because of the sheer number of sites we looked at, we can say with a fair degree of confidence that as area burned and wildfire severity increases, so too do the impacts on annual water yields.”

Bladon notes that for nearly a half-century through the late 1990s, wildfire trends were either holding steady or declining.

“All of a sudden there’s an inflection point and it goes up in terms of area burned,” he said.

“We had been spending as a nation $500 million a year fighting wildfires, and since 2000 that’s grown to the order of $2 billion a year. Suppressing and putting out wildfires now chews up more than half of the U.S. Forest Service budget. We need to find a way off that treadmill.”


 

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