Seminar: Land use change in regional climate modelling: The African Great Green Wall and the Apulia cases

Part of the Cycle of seminars: Understanding and managing climate risk

Land use change in regional climate modelling: The African Great Green Wall and the Apulia cases

The role of vegetation and land-use change in climate modelling is fundamental for accurately estimating surface energy fluxes and carbon budgets. Land-use and land-cover changes (LULCCs) can significantly modify surface energy and water exchanges, potentially affecting both regional and remote climates, depending on the spatial extent and intensity of the changes. Moreover, the climatic impacts of LULCCs reveal strong model- and region-dependent variability. Here, two case studies are presented: the African Great Green Wall and the Apulia region in southern Italy.

The Great Green Wall (GGW) is a multibillion-dollar African initiative aimed at combating desertification and restoring degraded land for the benefit of local communities. However, the potential climatic impacts of the most recent GGW implementation plan over northern Africa have not yet been comprehensively assessed. High-resolution (~13 km) simulations were conducted using the regional climate model CRCM/GEM4.8, considering four GGW scenarios with varying vegetation densities under two contrasting concentration pathways (low and high). Higher vegetation-density GGW scenarios lead to increased precipitation, reduced drought duration, and lower summer temperatures extending beyond the GGW region compared to the no-GGW baseline. All GGW scenarios, however, exhibit an increase in extreme hot days and higher heat indices during the pre-monsoonal season. Additionally, the simulations indicate a shift in Atlantic tropical cyclone genesis from the subtropical and western Atlantic toward the eastern Main Development Region under medium to high vegetation-density scenarios, while no significant GGW-induced changes are detected in cyclone intensity, translation speed, or other basin-wide tropical cyclone metrics.

The Apulia region was selected as a second case study due to the urgent need to reconsider land management strategies following widespread tree mortality caused by Xylella fastidiosa infestation. Two sensitivity experiments representing deforested and afforested conditions were compared with two control simulations (during present-day and future climate) under a high-emission concentration pathway. The experiments were performed using two regional climate models, CRCM/GEM4.8 and RegCM5. The results indicate that although rewilding may exacerbate temperature extremes, increased tree cover enhances soil moisture retention, thereby counteracting the progressive aridification of the region.

Overall, these experiments highlight the critical role of vegetation and LULCCs in driving significant climatic impacts that can extend well beyond the area of the projects, potentially influencing the large-scale circulation patterns and teleconnections, affecting climates in far-removed regions.

Contact: Marco Gaetani — marco.gaetani@iusspavia.it