Influence of bushfire on accumulation and ablation of a marginal montane snowpack in Snow Gum forests

Abstract

Forests modulate energy reaching the Earth’s surface. They can change energy balance fluxes, near-ground meteorological conditions, and seasonal snowpack properties in montane areas. Regions of forests cover are often collocated with areas of freshwater importance for ecosystem and anthropogenic uses. As such, alteration of forests in these regions has the potential to significantly impact water resources that many depend upon for daily life. Warmer climates with marginal snowpacks are known to be particularly vulnerable to impacts of climate change that may increase air temperatures and change precipitation. Similarly, montane forests are also becoming increasingly susceptible to modification by wildfire. This study measured energy fluxes, rates of snow accumulation and ablation, and applied (energy flux adjusted) physically-based snowpack models to examine fire alteration of snowmelt yield. Analysis focused on differences between an undisturbed and fire-disturbed forest stand, and referenced an unforested site. Fire-disturbance of forest canopy enhanced ablation rates by 53% relative to the undisturbed site. SWE storage and snowpack longevity were greater at the undisturbed forest, with seasonal snowpack in the fire-disturbed forest stand existing for 19 fewer days and at the unforested site for 32 fewer days. Overall, our results are congruent with canopy disturbance by fire having the impact of reducing snow accumulation (50 mm less SWE over two seasons, 4% reduction), enhancing ablation through increased evaporation (1% higher at the fire-disturbed site), and less total snowmelt available for runoff (38% less at the fire-disturbed stand). These results have significant implications for montane forests, and quantifies how they modulate energy fluxes, increase snow accumulation, seasonal snowpack longevity and melt volume, and how the impact of fire can persist for decades after burning and leads to reduced sub-alpine snow accumulation and melt.