Hydrological response of wildfire affected Mediterranean watersheds

Wildfires significantly alter the hydrological characteristics of forested catchments, including those in Mediterranean environments, that are typically adapted to fire disturbance. These changes can lead to increased hydraulic and hydrogeological risk until pre-fire conditions are fully restored. Despite their relevance, long-term experimental investigations of post-fire hydrological response in small Mediterranean catchments remain limited. This study investigates the post-fire variation of runoff response in four small, forested, hilly catchments in Central Italy. Immediately after the wildfire events, the catchments were instrumented with hydrometric sensors, enabling the monitoring and analysis of runoff response over time. A total of 108 runoff events were analyzed across the four instrumented catchments, each evaluated independently to account for the specific hydrological response of each basin. The Rational Method was applied to multiple real rainfall events to evaluate runoff coefficients and peak discharges through inflow-outflow relationships. Hydrological monitoring continued over a 6-year period, revealing an initial increase in runoff coefficients due to fire-induced alterations. However, a rapid recovery was observed within the first post-fire year across all catchments, with the runoff coefficient decreasing from peak values of around 0.8 to about 0.2, and full hydrological restoration occurring after another 5 years, when values stabilized around 0.1. The rapid decline in the runoff coefficient in the first few years following the fire is mainly due to the rapid vegetation recovery. These results improve the understanding of post-fire adaptation mechanisms, which could support the development of risk mitigation and land management strategies in Mediterranean catchments.