Wildfire impact on Boreal hydrology: empirical study of the Västmanland fire 2014 (Sweden)

Abstract. Land cover changes at watershed scale constitute key issues in general hydrology. Wildfires are one of the drivers of the changes in vegetation, which might affect hydrological fluxes and the water balance. The Västmanland fire in central Sweden burned 14 000 hectares and removed the Boreal forest in this area during the summer 2014. In here, we have studied the change in flow signatures during 3 years after the wildfire. In the empirical experiment we used a paired catchment methodology to compared 2 catchments highly affected by the wildfire with 2 unaffected catchments nearby, of similar character and climate to avoid the impact of natural variability in the analysis of wildfire impact. The average size of the catchments is 20 km² and a total of 23 catchment characteristics of flow and physiography were defined, trying to isolate each of the hydrological processes affected by the wildfire. We used both in situ flow measurements and remote sensing information (e.g. yearly volume at the outlet of the subbasins, fraction of vegetation or fraction of snow). The results show a change in the snow dynamics over the burnt areas with shorter duration of the snow season and a higher stream flow during autumn. This is probably related to an earlier snowmelt due to an increase indecent solar radiation over the snow cover without the canopy and the change in interception and transpiration from vegetation after the wildfire, respectively.