LINKING BURN SEVERITY TO SOIL INFILTRATION AND RUNOFF IN AN MONTANE WATERSHED: BOULDER, COLORADO

Dramatic increases in the wildland-urban interface has increased the risk of wildfires, and resulted in post-wildfire floods affecting homes and communities. As a result of this increase, wildfires burn ~ 3.5 million ha every year in the United States. The Fourmile Canyon Fire was ignited northwest of Boulder, Colorado, in September 2010 and burned for eleven days. The fire burned approximately 26 km2 and destroyed 169 homes in the area of Fourmile Creek, a primary tributary of Boulder Creek. Because wildfires do not have a uniform effect on a burned area, significant variability occurs between areas of different burn severity and likely different hydrologic responses within a watershed.

Soil is a major controlling variable of the hydrology of burned and unburned watersheds. Establishing a linkage between soil infiltration and burn severity may, therefore, offer insight into the likelihood of elevated levels of runoff and the likelihood of floods. Although previous studies have sought to establish a quantitative relation between runoff and burn severity, this relation has not been evaluated with respect to antecedent soil moisture in a montane watershed, such as the Loretta-Linda Basin. This study focused on linking burn severity to the runoff response and soil infiltration within the Fourmile Canyon burned area by comparing data collected from adjacent sub drainages of the Loretta-Linda Basin. These sub drainages though immediately adjacent to one another experienced different burn severities and was used to compare the short-term hydrologic response between areas of low and high burn severity. Rainfall, soil moisture, runoff, and infiltration data collected over a three month period were used to establish a quantitative relationship between burn severity, runoff and soil moisture. Initial investigation suggests that there is a correlation between high burn severities and low antecedent soil moisture levels and subsequent increased runoff.