Dr Roberto Ingrosso - The regional climate impacts of the Great Green Wall in northern Africa

The Sahel, a region on the southern border of Sahara Desert, has been considered one of the most important regional climate change hotspots throughout this century. The area was hit by severe droughts during the 60s and 70s, that combined with an increase in population, led to prolonged famines in the region. In order to fight against potential future desertification and land degradation of the Sahel, a range of stakeholders, including national governments, international organizations, the business sector and the local population, came up with a fascinating and complex project: the Great Green Wall (GGW). This African initiative is based on the afforestation of about to 7,000-kilometre-long stretch of degraded land from Senegal in West Africa to Djibouti in the east, with the objective of changing its hydrological cycle, increase local rainfall. In recent years, only a handful of studies have explored the potential effect of a Sahelian green belt project, finding significant changes in temperature and precipitation at a regional scale. However, the previous experiments were highly idealised and did not properly represent the modern project of GGW, being experimental designs more related to the initial project of the GGW as a forest belt extending from Dakar to Djibouti, for 7,000 km in length and 15km wide. In this talk, I will present the preliminary results of a realistic and more extreme GGW over the Sahel under current and future (RCP8.5) climate conditions, from simulations carried out with the Global Environment Multiscale (GEM) atmospheric model. However, as the GEM shallow convection scheme poorly reproduces the rainfall associated with the West African Monsoon (WAM), we also performed the experiments adopting the convection scheme used in the nested limited-area model (LAM) version of GEM (CRCM5), which better reproduce the WAM. We will then present the WAM sensitivity to the GGW using the two different convection schemes.