Forest fires can have a significant effect on the amount of water flowing in nearby rivers and streams, and the impact can continue even years after the smoke clears.

Now, with the number of forest fires on the rise in the western U.S., that phenomenon is increasingly influencing the region’s water supply—and has increased the risk for flooding and landslides—according to a UCLA-led study published this week in the Proceedings of the National Academy of Sciences.

Researchers, including coauthor Ben Livneh, CIRES Fellow and director of the Western Water Assessment, examined streamflow—a measure of water volume over time in rivers and streams — and climate data for 179 river basins. (Basins are areas of land where precipitation collects and drains into a common outlet.) All of the areas were located in the western U.S., and all had been affected by forest fires between 1984 and 2020.

Using a mathematical model they developed, the scientists discovered that streamflow in the years after a fire tended to be higher than scientists would expect based solely on climate conditions, and that larger fires tended to be followed by larger increases in streamflow.

In basins where over 20 percent of the forest had burned, streamflow was 30 percent greater than expected based on climate conditions, on average, for an average of six years.

Continue reading this story on UCLA's site here.