The fires that burned parts of Northern California in 2020 and 2021 took lives, destroyed buildings, and hurt air and water quality. A new study led by scientists at the U.S. Geological Survey California Water Science Center looks at another effect of these fires: how they changed the amount of water moving through the upper Feather River watershed.

This watershed drains into Lake Oroville, a key part of the State Water Project. The North Complex, Dixie, and Sugar Fires burned more than half of it.

Trees and other plants pull water from the soil and release it into the air. After the fires, there were fewer plants using water, so more water stayed in the soil or flowed into streams. The scientists measured this change by running a computer model with and without the fires’ effects on plants.

In water year 2023 (October 2022 through September 2023), the model showed about 1 million more acre-feet of water available for streamflow and groundwater because of the fires. That is almost a third of Lake Oroville’s capacity. The increase continued the next year, at about 690,000 acre-feet. Water year 2023 was also very wet, which makes it hard to separate the effects of the fires from the effects of the extra rain and snow.

“Wildfires cause real harm, and we aren’t saying they’re good for California. Our study shows that when a fire changes a forest, it can also change how much water reaches our streams and reservoirs. Understanding that change can help water managers turn a negative into a positive,” said Diana Zamora-Reyes, a U.S. Geological Survey scientist and the study’s lead author.

The study suggests that forest thinning and controlled burns may help make the water supply more reliable as rain and snow decline.

Read the full, free article, “The flip side of destructive wildfires: a water supply buffer to climate change,” in Environmental Research: Climate.