Burn Scars Lead To Deeper Snowpacks & Higher Flood Risks, Study Says

PROVO, Utah – Wildfires devastate forests across Utah each summer and researchers at Brigham Young University have discovered burn scars from those fires can lead to deeper snowpacks that provide more water for Utah’s reservoirs.

However, they also make areas more vulnerable to flooding and debris flows, according to the new study from BYU biology professor Sam St. Clair.

“As the fire becomes more severe and there’s more tree mortality or death, there’s less area to intercept the snow,” St. Clair said. “So more of the snow ends up on the ground. The snow is deeper and holds more water which fills our reservoirs.”

St. Clair studies the relationship between wildfires and water supply through the influence of wildfires on snowpacks. For this study, one graduate and four undergraduate students worked on backcountry skis, gathering data in central Utah’s Tushar Mountains over the last two winters.

“They slept out in sub-zero temperatures, very cold nights and skied up to 15 to 20 miles a day collecting the data,” St. Clair said.

They measured snowpack in the footprint of the Twitchell Canyon Fire, which wiped out 45,000 acres of forest in 2010.

“Some areas don’t burn at all. Some areas burn in a really severe way,” St. Clair said.

Before the fire, the dense forest reduced the depth of the snowpack because pine needles and tree branches suspended snow above the ground. On a day like Tuesday, that snow would evaporate.

“So that snow never actually hits the ground, never flows into a watershed and never ends up in our reservoirs,” St. Clair said.

After thousands of trees were wiped out by fire, that snow now adds to the snowpack on top of the burn scar. The researchers recorded 85% more snowpack in the areas where the trees burned completely compared to areas with no fire damage.

“That’s a good thing if that snow melts at the right time,” St. Clair said.

However, the loss of the forest, which led to the deeper snowpack, also eliminated the shading from the forest. So the snowpack is melting quicker.

“Some of that snowpack can be lost earlier and faster which can result in flooding, erosion and outcomes that we don’t want,” St. Clair said.

That can be critical information in the spring, when the potential for debris flows and mudslides rises.

“Understanding that the more severe the fire, the more snow accumulates,” St. Clair said. “We can then begin to map out areas that are going to be vulnerable and areas where there are going to be opportunities to accumulate more water in our reservoirs.”