Wildfire and topography impacts on snow accumulation and retention in montane forests

Abstract

Wildfires are increasing in frequency, severity, and size in many parts of the world. Forest fires can fundamentally affect snowpack and watershed hydrology by restructuring forest composition and structure. Topography is an important factor in snowpack accumulation and ablation as it influences exposure to solar radiation and atmospheric conditions. Few direct measurements of post-fire snowpack have been taken and none to this date that evaluate how topographical aspect influences the effect of forest fire on snowpack accumulation and ablation. We set up a two-year experiment on the Twitchell Canyon fire in south-central Utah on both north and south facing aspects and burned and unburned forest conditions across three replicated blocks. There was a significant interaction between burn condition and aspect for snow depth in which there was a reduction in snow depth in burned areas on south facing aspects but not on northern facing aspects. Snowpack disappeared earlier in burned areas than unburned areas, particularly on south facing slopes. Snow water equivalence (SWE) did not vary between burned and unburned forest. Year and topographical aspect were primary drivers of both snow depth and SWE. A review of five similar studies suggests that sites at southern latitudes and lower elevations could be more susceptible to reduction in snowpack after wildfire.