PERTURBATION AND RECOVERY OF SOIL HYDRAULIC PROPERTIES ACROSS A CLIMATE GRADIENT IN BURNED AREAS OF NORTHERN CALIFORNIA AND NEVADA

Wildfire perturbs the hydraulic properties of soils, leading to increased runoff, sediment entrainment, and probability of debris-flow generation in recently-burned areas. However, the degree to which the magnitude and longevity of this perturbation varies across climate zones is not well-understood. As the amount of recently-burned area in the Western U.S. continues to increase, measurements of soil hydraulic properties and subsequent timescales of recovery will be important for accurate prediction of debris-flow hazards, especially in regions with sparse data on burned soil properties and debris-flow occurrence. One such region is the northern Sierra Nevada, containing many recent wildfire scars spanning a wide range of mean annual precipitation and annual peak rainfall intensities. In this study, we present multi-annual field-based measurements of saturated soil hydraulic properties from five wildfires that burned in upland areas of northern California and Nevada. We also use an extensive dataset of laboratory-based soil-water retention measurements from these sites to assess possible sources of error that may confound traditional interpretations of infiltration data in burned soils. Our results provide new insights into the magnitude, longevity, and spatial variability of soil perturbations induced by recent northern Sierra wildfires. Such a dataset will be essential for understanding how the post-wildfire debris-flow hazard may vary as wildfires expand into cooler and more humid climates in the Western U.S.