Highly variable post-wildfire streamflow response across monitored contiguous watersheds

Wildfires can contribute to flooding, debris flows, and fluvial sediment transport that can impact downstream infrastructure and aquatic habitat. With increasing wildfire risk in the western U.S., understanding watershed-scale post-wildfire impacts on streamflow response and their controls is critical. Recent research has focused on small-scale process changes, but immense spatial variability in watershed and burn characteristics and temporal variability in recovery rates raises questions about the transferability of these studies. Existing watershed-scale field data is scarce since burned landscapes are highly dynamic and difficult to monitor. Here, we focus on the Grizzly Creek Fire (2020), which burned 132 km2 and impacted multiple tributary watersheds of the Colorado River through Glenwood Canyon, CO. Within the past year since fire, post-fire erosion and flooding has impacted critical infrastructure within the canyon, including the I-70 highway and railroad corridors, Shoshone hydroelectric power plant, and the municipal water supply. The burned watersheds exhibit distinct characteristics (elevation, slope, aspect, drainage network shape), flow regimes (ephemeral, baseflow driven, snowmelt driven), and burn attributes (percent burn area, severity). Rainfall and streamflow monitoring equipment was installed immediately following fire in five burned watersheds and two contiguous unburned watersheds. Initial field data has revealed distinct post-fire streamflow responses to snowmelt and summer monsoon storms between the five watersheds. This study demonstrates the importance of a watershed-scale perspective and the value of increased post-fire field monitoring efforts (despite the multitude of challenges). Identified relationships between watershed, burn characteristics, and streamflow response at the Grizzly Creek Fire will inform local post-fire mitigation and management strategies, as well as support future work characterizing post-wildfire streamflow response patterns across western watersheds.