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.

Monitoring and Quantifying Soil Erosion and Sedimentation Rates in Centimeter Accuracy Using UAV-Photogrammetry, GNSS, and t-LiDAR in a Post-Fire Setting

“…According to [13], the runoff rate increased three times and the soil loss was doubled after the forest fire in Spain. Previous research [17,18] showed that for the hillslope sediment yield balance, three to five years are usually required, while others [147] denoted the increase in sediment yield before and after the wildfire of 2009 in the Penteli region (Lykorrema watershed), where a mean pre-fire value of 0.02 t/ha/yr was replaced by a mean post-fire value of 0.13 t/ha/yr (for 2009-2014 estimation). The results displayed in this article are in agreement with previous researchers, showing that, in the Mediterranean conditions, the maximum soil erosion susceptibility is recorded within 4-6 months after the fire [148,149], as depicted in the Ilioupoli test site.…”

Integrating Remote and In-Situ Data to Assess the Hydrological Response of a Post-Fire Watershed

“…Despite the fact that the scientific literature describes a wide spectrum of empirical formulations [49][50][51], in this integrated approach, the Natural Resources Conservation Service-Soil Conservation Service (NRCS-SCS) method [41,52] was used. This method, described by Equation (7), directly depends on the length of the main water stream L (km), while it is inversely proportional to the average slope of the watershed (m m −1 ) and CN:…”

“…The ability to survive and re-sprout depends on tree height, scorch and char heights, tree species, age, stem and bark thickness, and fire intensity and residence time. In the hydrological cycle, this natural process leads to a reduction in evapotranspiration fluxes, leaf rainfall interception and tree suction capacity [7]. High temperatures can vaporize soil organic matter and generate a thin hydrophobic layer (from 1 to 7 cm), which strongly reduces soil infiltration capacity [8].…”

Conceptual Model for Integrated Meso-Scale Fire Risk Assessment in the Coastal Catchments in Croatia

“…However, wildfires, i.e., extreme free-burning fires, have a significant impact on ecosystems' natural balance [2,3]. Fires affect ecosystems, causing change in vegetation patterns, soil properties, and hydrological processes, consequently altering the watershed conditions and water quality and hence posing a threat to water supply sources [4][5][6][7][8]. They also have a devastating impact on property, infrastructure, and populations' health and lives.…”