Hydrological Response of Natural Mediterranean Watersheds to Forest Fires

Abstract

Fires are common in forested Mediterranean-climate watersheds. Forest fires cause abrupt land use/cover (LULC) changes affecting soil properties and hydrological processes within and across watersheds. A major forest fire in Attica, Greece, that affected the Lykorrema stream experimental watershed provided the opportunity for an in-depth study of the impact of forest fires on the hydrological balance of natural Mediterranean watersheds. To this end, detailed hydrometeorological data recorded for five years before and for five years after the fire incidence were utilized. SWAT model was also used to consider the potential influence of meteorological conditions temporal variability on the results of the analysis. Specifically, SWAT model was parameterized calibrated and validated for the pre-fire and the post-fire conditions using the corresponding detailed hydrometeorological data for the respective periods. Then the two versions of the model were applied for the entire period providing comprehensive time series for all the flows and storages in the studied watershed. In this way, the post-fire LULC and soil properties changes were the only influencing factors driving the alterations in the hydrological balance allowing an impartial comparison. The obtained results highlighted the considerable impact of forest fires on the watersheds’ hydrological functioning. Specifically, the maximum direct runoff depths and the maximum flow rates were substantially higher in the post-fire conditions. In contrast, actual evapotranspiration was reduced, when the effect of fire was considered. The obtained results indicate that the altered post-fire LULC and soil properties are major drivers of the watershed’s hydrological balance changes. SWAT model performed sufficiently well for both the pre- and post-fire conditions and provided a deeper insight into the impact of forest fires on the hydrological functioning of natural Mediterranean watersheds.