Warming temp, reduced snowpack, increased fire risk, impact of 1° warming?

Climate models may be underestimating a vicious cycle in northern forests where warming temperatures and reduced snowpack can increase fire risk and potentially cause permanent damage to ecosystems.

Northern Arizona University ecologist Andrew Richardson led a new study of long-term warming experimental results, finding that even slight increases in temperature in the boreal forests can lead to a significant reduction in snowpack. The Journal of Geophysical Research: Biogeosciences has published the research.

Less snowpack results in the soil absorbing more light and heat. This absorption further increases the ground temperature, leading to warmer air temperatures and increased snowmelt. Consequently, this rapid change affects the boreal forest, stretching across the northern half of three continents and hosting many critical ecosystems, at a much faster rate than scientists previously realized.

Less snow, warmer ground, impacts

"Snow is really a critical part of winter in most northern ecosystems," said Richardson, a Regents' professor in the School of Informatics, Computing, and Cyber Systems and the Center for Ecosystem Science and Society.

"Transitioning to low- or no-snow winters is going to have major implications for how these ecosystems 'work.' We'll likely see negative impacts of low snow, such as frozen soils and damaged plant tissues, as well as reduced spring runoff and drier soils going into summer. Even if you don't like winter, this is just bad news all around."

The researchers tested their hypotheses using the U.S. Department of Energy's SPRUCE Experiment in northern Minnesota. They used large experimental enclosures, 30 feet wide and 20 feet high, to simulate future climate conditions. They manipulated air and soil temperatures using fans and heaters.

The researchers used time-lapse digital photography to monitor conditions in each enclosure every 30 minutes, and estimated snow depth and cover from the pictures. The researchers compared these results to historical data on snow depth and precipitation, enabling them to get a better picture of the effects of temperature changes on the ecosystem and changes in snow albedo, or reflectivity, which can affect soil and air temperatures.

Less snow, more rain, and a short-lived snowpack

They learned something not exactly surprising: a temperature rise caused more snow to melt. The snowmelt's severity surprised them; they discovered that any degree of warming, no matter how minute, caused the snow cover to drop precipitously. This caused changes in the plant life and soil ecosystems of the boreal forest, leading to increased plant stress and mortality.

This particularly important implication for climate modelling means that we can use the results from this study to evaluate the adequacy of current models in simulating the effects of warmer temperatures on the extent and duration of snow cover. Since temperature is the only variable, they could capture data, which is impossible to isolate in the real world.

"Although northern Arizona doesn't sit within the boreal forest, these findings likely predict a future with fewer snowy winters, more rainy ones, and a snowpack that doesn't last as long."

"Already, we're close to the edge—you just have to compare the usual larger amount of snow at the Flagstaff Nordic Center, which is slightly higher in elevation, to the snow in town," said Richardson. "While it might seem like good news for residents tired of snow by the end of January, it possibly signifies heightened stress for our forests." "As someone who loves winter, I perceive less snow and more fire danger as a double dose of bad news."

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