Vegetation–atmosphere feedback in the Mediterranean region from Regional Climate Model simulations: the Apulia case study

Over the past three decades, the Mediterranean region has experienced an increasing frequency and duration of drought events, a trend that is projected to intensify as anthropogenic emissions continue to rise. Available evidence indicates that drought conditions can trigger extensive tree mortality, amplify wildfire risk, and drive a progressive shift from Mediterranean ecosystems toward vegetation characteristic of semi-arid regions. The role of vegetation and land-use change in climate modelling is fundamental for estimating surface energy fluxes and carbon budgets. Land-use and land-cover changes (LULCCs) can alter surface energy and water fluxes, potentially leading to different responses in mean and extreme temperature and precipitation based on different representation of the vegetation. Apulia, in southeastern Italy, is an ideal case study, having experienced massive olive tree die-off due to Xylella fastidiosa, an invasive pathogen detected in 2008. This vegetation loss is compounded by increasing drought impacts. This case offers a unique case study to assess the consequences of extensive olive trees die-off after the spread of the pathogen/bacteria Xylella fastidiosa. In order to assess potential impacts of significant change in vegetation covers, we investigated the effect of die-off and of massive replanting on the regional climate. The study involves two vegetation scenarios (deforestation and reforestation) performed with four sensitivity experiments at 12 km horizontal resolution with two different regional models: RegCM5 and CRCM/GEM4.8. Two experiments will serve as references for present-day (PD, 1990-2019) and future (2071-2100), while other two future experiments will be performed under both vegetation change scenarios. The percentage of plant functional types in the land component (CLM4.5) of RegCM was replaced with that used in the CRCM/GEM4.8 simulations. Preliminary results show that while temperature extremes can be exhacerbated by rewilding, increasing tree cover can help to keep soil moisturised, acting against the progressive aridification of the area. On the other hand, the deforested case leads to a decrease in daily maximum temperature, particularly in Fall and Winter and an increase in daily minimum temperature in Summer. These changes are driven by albedo feedback related to the land-use modification.