IMPACT OF BURNING ON HYDROLOGIC RESPONSE AT THE LABORATORY SCALE

As climate continues to shift, the present wildfire regime in the Western US is expected to change with increasing fire frequency and intensity triggered by warmer temperatures, earlier snowmelt, and decreased snowpack. As burned ecosystems become increasingly common, it is critical to better quantify how fire impacts infiltration, soil moisture, and near-surface flow. Here we present the pilot results of a laboratory investigation into the impacts of wildfire on soil and hydraulic properties, such as water repellency and hydraulic conductivity. The aim of this work is to measure hydrologic response in burned soils under controlled laboratory conditions using undisturbed soil cores with a surface area of 325 cm² and a minimum depth of 10 cm. Very few studies have used intact soil samples and maintained the natural soil structure, including preferential flow paths, that we believe will be important in quantifying the impacts of burning on these parameters. These soil samples were collected near the Boulder Creek Critical Zone Observatory from soil that has not experienced wildfire in recent history, but is near the 2010 Fourmile Canyon Fire burn area and is well within the Southern Rockies ecoregion that commonly experiences wildfire. Laboratory burning of the samples was designed to simulate the intensity and duration of low, moderate, and high severity fires that might be expected for this system. To emulate natural fire conditions, samples were burned from above using both flaming combustion and application of a heat gun. Soil sample temperatures were measured at the surface with an infrared thermometer and below the soil surface with thermistors. The intensity and duration of the rainfall simulation experiment were also chosen to represent a precipitation event that might occur after a wildfire in this ecoregion.