Assessment of Basin Vulnerability to Post-Wildfire Hydrologic and Water Quality Effects Through a Multi-Scale Framework

Brucker, Carli P.

Graduate Thesis Or Dissertation

Assessment of Basin Vulnerability to Post-Wildfire Hydrologic and Water Quality Effects Through a Multi-Scale Framework Public Deposited

Analytics

Download PDF

Citations

Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/cv43nz221

Abstract

Wildfires can present challenges for water treatment plants and freshwater systems by increasing sediment, nutrient, and dissolved organic matter (DOM) loads in streamflow, as well as driving increased runoff rates. Although these effects are well known, high variability and data scarcity in post-wildfire in situ water quality observations have created challenges in analyses and predictive efforts. This dissertation attempts to increase knowledge of burn impacts on water quality and supply through a multi-scale analysis—observing small-scale driving mechanisms as well as broad, large-scale response across multiple watersheds. Underlying processes driving soil and water physical and chemical changes were first observed using laboratory-scale wildfire and rainfall simulation experiment apparati, tested on 154 ~300 cm² soil samples. Burn effects were observed both independently, as well as in the context of other key drivers—rainfall intensity and terrain slope—to simulate variable conditions in natural settings. Runoff and sedimentation rates showed significant (α = 0.05) monotonic increases from mild to severe burn intensities, while dissolved organic matter and nitrogen concentrations had significant inverse ‘U’ shaped trends, peaking at ~250°C with values 201-266% of unburned samples. A synthesis of previous laboratory- and plot-scale wildfire simulation methods was also completed, where benefits and limitations of different techniques were discussed. Future studies were recommended to prioritize representation of natural processes, incorporation of multiple key drivers, analysis at multiple spatial scales, and uncertainty quantification based on their scale, scope, and subject matter. Next, broad changes in constituent responses in post-fire years were assessed for 241 forested watersheds across the U.S. West using machine learning and statistical techniques. Inter-basin variability in post-fire responses was also characterized and attributed to physiographic watershed variables and wildfire characteristics. Significant responses were observed in the first 2-3 years post-wildfire for carbon, nitrogen, and phosphorus constituents, and up to six years for sediment constituents and turbidity, with forest cover highlighted as a driver of response variability. By analyzing both small-scale driving mechanisms, as well as broad effects across a large regional scale, this dissertation strives to provide a holistic understanding of wildfires’ impacts on watersheds in the U.S. West. Key insights into the duration of elevated responses, as well as key factors exacerbating wildfire effects may help inform water managers’ planning and mitigation efforts.

Creator