SALT LAKE CITY — A new study by Brigham Young University shows that mountain landscapes charred by wildfire dramatically accumulate more snowpack — 85% greater depth — than areas untouched by wildfire.
That information is critical to water managers, wildfire ecologists and even downstream communities that may have to prepare for flooding as the additional snowpack melts when the weather warms up.
Led by BYU professor Sam St. Clair and published in Environmental Research Letters, the study was the first of its kind to analyze the effects of burn severity on snowpack accumulation and the amount of water in that snow using direct measurements.
St. Clair said the findings have wide-ranging implications for forecasting water supply, especially since in Utah, mountain watersheds provide 65% of the state’s water resources.
“We know that fires create a mosaic of burn severity,” said St. Clair, a professor of plant and wildlife sciences, pointing out the complex nuances of a wildfire’s aftermath present challenges that impact wildlife, vegetation, the ranching industry, water resources and the communities around them.
“We can use this information to make more informed decisions.”
When wildfires destroy a forest canopy, consuming trees — particularly conifer — they wipe out a natural shield that accumulates snow on its branches and absorbs the moisture.
“Fires mean more snow into the system initially because of reduced trees that usually block and hold the snow temporarily on branches,” St. Clair said.
“It’s a really good outcome for north-facing slopes where the snowpack will hold in the shade, but if you’ve got a south-facing (sun-exposed) aspect with a deep snowpack and a rapid spring melt, now there is a higher chance of erosion, loss of nutrients and potential of flooding for downstream communities,” he said. “The larger and more severe the wildfire, the increased flood potential for valleys.”
The research also revealed a 15% increase in snow-water equivalent — the amount of water contained within the snowpack — for every 20% increase in tree mortality in the burned areas.
Carried out over 30 months, the research focused on the effects of the Twitchell Canyon Fire that burned 45,000 acres in 2010 in the Tushar Mountains about three hours south of BYU’s Provo campus.
Doctoral candidate Jordan Maxwell and two other students covered 10 to 15 miles each day backcountry skiing, measuring snow depth and water content in 30 locations.
St. Clair said the findings also demonstrate the “indirect” effects of wildfires and how they impact forest ecology, such as charred, darkened landscapes that accelerate snowmelt and not only impact what water flows downstream to waiting reservoirs, but what water stays in the mountains.
“Wildfire regimes are changing forest ecosystems, and now we know they’re impacting water hydrology, too,” St. Clair said.