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Climate and Environment

Wildfires Are Altering Streamflows In The Western US

A charred sign shows fire danger as very high
A sign showing fire danger levels is charred after the Station Fire swept through the Angeles National Forest in 2009.
(Justin Sullivan
/
Getty Images)
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It's no secret that fires have increased in the West over the past few decades. But what effect will that have on the water supply?

Park Williams, an associate professor at UCLA's department of geology, led a study that found big fires increased water streamflow on average by 30% over the span of six years in areas where more than one-fifth of its forest burned.

Williams says fires remove forest cover, which leads to forests using less water. On top of that, soil can get cooked during blazes and repel water, leading to enhanced streamflows.

He says this phenomenon applies to the Sierra Nevada.

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"We think that in the Sierra Nevada, now we're kind of on the precipice of fires being large enough in recent years to actually change the math about how much water is coming out of the mountains and into our lakes in California's Central Valley," Williams said.

All of this could be good news. More water might become available amid the drought, Williams pointed out.

But at the same time, water — post-blaze — can become polluted with large sediment and debris loads, and mudslides can increase, as well as other hazards.

And water managers face increased pressure. Every fall and winter, overseers decide how much water needs to be let out of lakes at the base of the Sierra Nevada to make room for the possible giant storm that could lead to a massive rush of water coming into the lake all at once.

"And if they don't make that calculation accurately, they could end up with situations where lakes are overtopping — kind of like what happened in 2017 with Lake Oroville when that lake nearly overflowed, and then they had the damaged spillway and had to evacuate many thousands of people because of the flood risk."

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Williams hopes his research can help managers determine how much water falls in the mountains and how much of that ends up in our streams.

That way, the extra water — brought upon by fires — can be used to its full extent.

What questions do you have about Southern California?