Hydrological behaviors of steep high water yielding Rocky Mountain's watersheds in response to wildfire

Understanding the impacts of forest wildfires on catchment hydrology is important for managing post-wildfire related hydrological risks. The unpredictable nature of wildfires makes it difficult to have pre- and post-disturbance data for analysis. So we often rely on post-wildfire response analyses techniques to characterize the changes to the hydrology. When only post-wildfire data are available differences in catchment characteristics and precipitation complicate the interpretation of the results. We present the analysis of data collected following the 2003 Lost Creek wildfire that burned in the eastern slopes of the Rocky Mountains in southern Alberta. These catchments are steep high water yielding, mountainous, similar in physical characteristics and contribute flow to the Oldman River, which is an important source for irrigation and urban areas. We used precipitation, streamflow and snow course data from 2005-2011 for four catchments (two burned and two unburned) to describe possible effects to the water yield (monthly, seasonal and annual), flow duration curves, low flows, high flows, peak flows, and recession characteristics. We also use the concept of elasticity (a relationship between precipitation and flow usually used to examine the streamflow sensitivity to climate change) to account for the effects of spatially variable precipitation. Elasticity appears to be a useful concept for describing changes when only post-disturbance data are available. The March snow course data showed an increase in Snow Water Equivalent in the burned area when compared to the intact forest. We observed higher mean annual water yield and mean peak flows from burned catchments. The burned watersheds had earlier onset of spring peak, higher flows in spring (March, April, May) and lower flows in summer (June, July, August). Flow recession was also faster for the burned catchments. These results were expected, however the analysis indicated smaller changes to mean annual water yield and mean peak flow than other studies reported in the literature.