In snow-dominated regions globally, mountain snowpacks are a vital water resource for recharging aquifers (an underground layer of water-bearing material) and sustaining streamflow (the flow of water in streams and other channels) into the drier summer months. This natural course is being disrupted by human-initiated environmental changes.
Wildfires, themselves often a product of climate change, are causing earlier snowmelt across the western U.S., and this effect will only become further exacerbated by projected warmer winters. This presents increased environmental risk. Notably, wildfires are increasing in frequency, size, duration, and intensity.
A new study, from the Colorado School of Mines (a public R1 research university focused on applied science and engineering), concludes that snow that falls in forests that have been burned melts more quickly than snow that falls in forests that haven’t burned. The study has significant water supply implications for communities that rely on snowmelt to satisfy their water requirements.
The earlier snow melt in burned forests is a result of two processes. The darker snow left by forest fires is less reflective, causing the snow to absorb more energy and melt earlier.
Secondly, burned forests often have less tree cover, so there is more sunlight reaching the snowpack.
Additionally, climate change also affects the snow sensitivity to burned conditions. Here, colder winter air temperatures yield snowpacks with higher cold content (defined as the amount of energy required to melt a snowpack). This occurs throughout the winter, providing a higher energy threshold needed to melt the snow.
Impacted: Pacific Northwest and Northern Sierra Nevada
Climate warming has altered patterns of snow accumulation and melt throughout the seasonal snow zone in the western U.S. Lower elevation regions like the Pacific Northwest and Northern Sierra Nevada will be especially impacted. These changes could make it harder for communities there to manage their water supply.
The study relied on remotely sensed snow data gathered by NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) satellite. Most previous studies on the topic utilized ground-based measurement systems.
Postfire snow cover loss was shown to be more extreme in relatively low-elevation, warm environments compared to that in high-elevation, cold regions.
According to the study, 98 percent of forested regions in the western U.S. could expect earlier snowmelt after a fire occurs. The situation gets worse as average temperatures increase – with 2°C of additional warming, the type of warming predicted to accompany climate change, 86 percent of the snow zone would experience earlier post-fire snowmelt compared to historically average conditions.
The research appears in the journal Science Advances, titled “Impact of current and warmer climate conditions on snow cover loss in burned forests”.
