Wildfires can have a big impact on freshwater sources

A new study from Oregon State University (OSU) has found that large wildfires cause increases in river flow that can last for years or even decades. The research will provide insight for water resource managers as climate change is causing wildfires to become more frequent and intense.

Elevated stream flows can cause issues when they carry along contaminants following a fire. Study co-author Kevin Bladon is a hydrologist in OSU’s College of Forestry.

“People see and smell the smoke from fires and when it’s gone, they think it’s over,” said Bladon. “But actually the impacts on other values, such as water, are just beginning at that point.”

According to Bladon, more than two-thirds of municipal water systems in the United States get their drinking water from a source that originates in a forest.

“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,” said Bladon.

“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.”

The researchers analyzed 30 years of data regarding fires, climate, and river flow from 168 river basins across the United States. They found a significant increase in annual river flow in watersheds where more than 19 percent of the forest had burned.

The research also revealed that prescribed burns do not significantly alter river flows. Bladon said that this finding indicates that prescribed burns are an effective management tool because they can create more resilient forests without impacting water yields.

“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,” said Bladon.

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

The study is published in the journal Nature Communications.

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By Chrissy Sexton, Earth.com Staff Writer