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Increasingly Intense Wildfires Becoming More of a Threat to Water Supplies

Runoff from burned forested areas has shown to be a source of contamination.

Wildfires are destructive for obvious reasons and for some that aren’t as obvious: They can and do contaminate water supplies.

A recent report, co-authored by Fernando Rosario-Ortiz, associate professor at the University of Colorado’s Department of Civil, Environmental and Architectural Engineering, sheds some light on what is becoming acknowledged as a serious issue with more intense and numerous wildfires.

Many drinking water utilities get their water from forested watersheds, where wildfires are increasing and posing threats to the water supply.

Wildfires causing mudslides and sediment mobilization is common and widely acknowledged because of the imagery of homes and roads being destroyed. But the less visible and, thus, maybe less acknowledged, is water supply contamination.

“We know that where soil has been burned, the water doesn’t percolate through it so there’s more surface runoff,” Rosario-Ortiz said. “There have been a lot of people looking at inorganic contaminant nutrients for a long time, but what surprised me was that when we started doing some of the work in 2012, when it came to drinking water treatment, not a lot had been done.”

He said the fire in Colorado Springs in 2012 straddled water infrastructure. “That hit some water managers hard. That’s a worst-case scenario when you’re drawing drinking water from a pristine source and then all of a sudden here comes trouble.”

The trouble arrives after wildfires that remove vegetation from sloped areas and are followed by heavy rainfall, which runs off the slopes bringing nutrients, such as inorganic nitrogen. We’ve also measured metals in the water, sulfur organic matter, Rosario-Ortiz said. He said sulfur-organic matter is present in water everywhere, but wildfire contaminants can impact the chemistry of this matter and cause contamination.

The study looked at the impact of this contamination to help utilities understand how to treat the water when it occurs.

The forested areas of Colorado aren’t the only areas that should be concerned with water contamination resulting from wildfires with a warming climate. Rosario-Ortiz said there are United States Geological Survey maps that show that roughly about two-thirds of the watersheds in the country are forested watersheds.

San Francisco’s water supply comes from Hetch Hetchy Reservoir in Yosemite National Park. “We work with New York City, their water comes from the Catskill Mountains,” Rosario-Ortiz said. “There’s a model that shows that New York City in a few years will behave like North Carolina.”

Other cities, like Portland, Ore., may not feel the threat now but that could change as wildfires continue to increase and become more intense.

“We’re doing a much better job of mitigating these fires than before, but we’ve had to,” said Mike Myers, chief of the Colorado Springs Wildland Fire Team. “The fires now are just so much bigger and stronger than before.”

The city of Denver, and partners, is investing $66 million in tree thinning and reforestation in some watersheds. The report pointed to other short-term solutions, such as expanding water-shortage capacity, diversifying water sources and using pre-sedimentation basins.