Abstract
Studies simulating the large-scale afforestation of the African Sahel constantly find warning signals of increased risk of extreme temperatures and heatwaves resulting from changes in albedo and latent heat flow. We review the afforestation measures underlying three simulation studies, together with a restoration model in which compartments are formed by greenbelts to enable succession of savanna vegetation, protected from hot wind and drought. Savanna-like vegetation (around 20% woody plants) will show bright reflective surface and drying of leaves during dry season rather than constant green color, with very different impact on albedo and temperatures. We derive that the simulated risks of extreme heat and flooding from rain will strongly depend on species, shape and density of the new vegetation. Ecological restoration concepts are expected to mitigate or prevent such restoration related climatic risks. Compact afforestation of the Sahel does not appear to be necessary or feasible. A restoration model based on compartmentalization and the protected succession of diverse, climatically adaptable vegetation could also be used in populated drylands, as a sustainable and temperature balancing solution to desertification.
Highlights
“Great Green Walls” (GGW) are large ecological engineering projects of afforestation in semi-arid or arid desertification areas
We review the afforestation measures underlying three simulation studies, together with a restoration model in which compartments are formed by greenbelts to enable succession of savanna vegetation, protected from hot wind and drought
In this review we look into the assumed afforestation measures that some recent Sahel GGW simulation studies are based on, together with the land-use changes (LUC) resulting from the above compartmental revegetation model (Huebner, 2020)
Summary
“Great Green Walls” (GGW) are large ecological engineering projects of afforestation in semi-arid or arid desertification areas. Afforestation may aggravate extreme precipitation and flooding (Diba et al, 2016; Saley et al, 2019) so that decision-makers and politicians were warned to take these risks into account when planning large scale afforestation like the Sahel GGW (Diba et al, 2019). These concerns may contribute to a slow progress of this program in some African countries. We review the FAO dryland assessment of necessary restoration in the Sahel (Mansur, 2016) to understand how the Sahel climate simulations are related to the current plans of the FAO to create the African “Great Green Wall”
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