Wildfire effects on net precipitation, streamflow regime and rainfall-runoff events in northern Rocky Mountain watersheds
Creators: Williams, Christopher HS
Publisher: name: University of Alberta Library
Year: 2022

<p>In recent decades, severe wildfire in western North America has increased in frequency as a result of a warming climate and historical fire suppression, impacting an increasing amount of forested area. Reduced forest canopy interception and storage combined with soil water repellency and altered soil structure after wildfire can lead to greater runoff responses than in unburned forests. This has led to a proliferation of post-wildfire hydrological studies, mostly at the plot and hillslope scales, and mainly located in heavily impacted regions of the USA (e.g. Colorado, New Mexico, California). However, the more northern Rocky Mountain regions have also been subjected to warming and increased risk of wildfire. The eastern slopes of the Canadian Rocky Mountains provide a disproportionate amount of vital surface water supplies to the Prairie Provinces largely owing to high overwinter snow accumulation. Much less is known about post-wildfire hydrology and runoff response in these more northern, snow-dominated mountain regions. This study examined impacts from the 2003 Lost Creek wildfire on net precipitation, flow regimes, and storm rainfall-runoff events in Rocky Mountain watersheds in the Crowsnest Pass, Alberta, Canada. </p>

<p>Net precipitation was studied in subalpine forest stands while flow regimes and storms were studied at the watershed scale. Four subalpine forest stands (two burned and two unburned reference) were used to measure rainfall interception and snow accumulation (SWE); net precipitation was derived from these measurements for the study period (2005-2014). Mean net precipitation was 274 mm (51%) greater in burned than in unburned reference forest stands. Greater mean snow accumulation (SWE) and net rainfall, respectively, constituted 152 and 122 mm of this total. Studies focused on post-wildfire flow regimes at varying time intervals (annual, monthly, weekly) were conducted during the 2nd to 11th years (2005-2014) after the wildfire. Streamflow and precipitation were measured in three burned and two unburned reference watersheds in a replicated post-hoc study design to enable comparisons. Flow regime studies highlighted greater magnitude and earlier timing of snowmelt runoff in wildfire-affected watersheds – April and May water yields were 100-200% and 40-50% higher, respectively, and half-flow dates arrived approximately 7-10 days earlier in burned compared to reference watersheds. The effects of wildfire on storm runoff during the snow-free season (late June to late September) was more ambiguous but flow responses in burned watersheds were proportionally greater, in general, than those in reference watersheds. However, post-wildfire storm runoff was surprisingly muted compared to that from other wildfire-affected regions and multiple regression analysis suggested fire accounted for &lt;4% of the overall variability in runoff response. Despite greater net rainfall and snow accumulation at the forest stand level, effects to components of the flow regime and to storm runoff in burned watersheds were not large in comparison to results from studies in other regions.</p>