Understanding the hydrologic impacts of wildfire management strategies using MIKE SHE

Abstract:

Proactive thinning and controlled burning are being utilized to mitigate the effects of severe wildfires. Hydrologic function of watersheds after wildfires and clear-cutting has been well documented but the impacts of pre-fire mitigation strategies are less understood. We utilized two mixed precipitation watersheds, which supply drinking water for Ashland, Oregon, to assess the effectiveness of restoration and fuel reduction strategies on relative hydrologic change. This Mediterranean dry mixed conifer-hardwood habitat is unique as it sits in the convergence point of several ecoregions, providing significant biological diversity for the region. We evaluated the hydrologic response from prior mitigation strategies including max monthly flow, mean annual 7-day low flow, runoff ratios, timing and total water yield and found an average decrease of 26% and 24% in total annual water yields in the West and East basins of the Ashland watershed, respectively. Our analysis showed that 66% (West) and 72% (East) of the changes in water yield were due to annual variations in precipitation, demonstrating that land cover changes were not the dominant driver of hydrologic change. Current work includes identifying the thresholds at which stand density reduction leads to an increase in annual surface water yield. We utilize the integrated surface and groundwater model, MIKE SHE, and simulate a range of forest fire mitigation efforts based upon representative parameters in the model, including leaf area index. We will then expand our findings to stand density index for better interpretation of our findings to make recommendations for local and regional forest managers. Ultimately, our work aims to inform future implementation of forest restoration and climate adaptation at larger scales.