A wildfire’s legacy can haunt rivers for years, putting drinking water at risk

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Ben Livneh, University of Colorado Boulder

(THE CONVERSATION) A wildfire rages across a forested mountainside. The smoke billows and the flames rise. An aircraft drops vibrant red flame retardant. It’s a dramatic, often dangerous scene. But the threat is only just beginning for downstream communtiies and the water they rely on.

After the smoke clears, the soil, which was once nestled beneath a canopy of trees and a spongy layer of leaves, is now exposed. Often, that soil is charred and sterile, with the heat making the ground almost water-repellent, like a freshly waxed car.

When the first rain arrives, the water rushes downhill. It carries with it a slurry of ash, soil and contaminants from the burned landscape. This torrent flows directly into streams and then rivers that provide drinking water for communities downstream.

As a new research paper my colleagues and I just published shows, this isn’t a short-term problem. The ghost of the fire can haunt these waterways for years.

This matters because forested watersheds are the primary water source for nearly...