Processes induced by fires on geo-hydrological conditions and on water resources in the Monte Pisano area

This Ph.D. project investigated the effects of wildfires on forested watersheds, employing a multidisciplinary approach. The study focuses on the Monte Pisano Mediterranean mountainous ridge, near Pisa, Italy, which experienced two large wildfires in September 2018 and February 2019. The project examined medium to long-term consequences on hydrology, water quality, and soil properties of some instrumented watersheds. The study reviewed the paired watersheds methodology, suggesting the Euclidean distance calculation as a more rigorous selection method for burnt-unburnt watersheds to be compared. The hydrological analysis revealed increased runoff in the burnt watershed, which is confirmed by chemical and isotopic data. Water quality assessments show slight differences in trace metal concentrations between burnt and unburnt areas, and no differences in organic compounds. The study also addressed post-fire soil hydraulic properties. Field surveys demonstrate differences in saturated hydraulic conductivity between burnt pine tree forests and unburnt olive groves. Moreover, soil hydraulic properties were mapped based on morphology, lithology, and vegetation cover in one selected watershed. Finally, the work also evaluated annual precipitation regimes in northern Tuscany over the last century, highlighting changes since the 1970s, with the mountainous region experiencing a decrease in mean annual precipitation and a relation between topography and precipitation variations.