Revealing the importance of transpiration from trees and non-tree vegetation to moisture recycling over Africa

Abstract

The redistribution of biological (transpiration) and non-biological (interception loss, soil evaporation) fluxes of terrestrial evaporation via atmospheric circulation and precipitation is an important Earth system process. Overall, vegetation is the main contributor to terrestrial evaporation and subsequent precipitation over land. Yet, the specific contribution of different vegetation classes remains understudied. Here, we investigate how different vegetation classes (trees and non-tree vegetation) contribute to precipitation patterns through moisture recycling over African watersheds. Our study is based on simulated daily atmospheric moisture trajectories derived from the Lagrangian model FLEXPART, driven by 1° resolution reanalysis data over 1981–2019, aggregated at the monthly level. The data is constrained by evaporation and precipitation products, and unravels the annual and seasonal contribution from trees and non-tree vegetation to precipitation, employing fractional vegetation cover data. Our findings show that trees provide a higher water flux to precipitation over Africa compared to non-tree cover, with contributions of 777 mm year-1 versus  342 mm year-1  respectively. However, the large extent of non-tree vegetation over the continent compensates for this difference and many watersheds depend even largely on non-tree vegetation for precipitation. As non-tree vegetation appears to be important for precipitation over Africa, its current contribution to water availability should not be overlooked and requires further research, particularly in relation to ongoing land use and land cover change that may affect hydrology. Providing an outlook on existing and projected land use and land cover change, we highlight the spatial heterogeneous impact on local and regional water availability over the continent.