Abstract
In West Africa, surface atmosphere exchanges have been found to impact both regional and local features of the Monsoon. At local scale the spatial patterns of evaporative fraction can drive the trajectories of mesoscale convective systems. Within Sudanian climate, ~80% of the precipitation returns to atmosphere through evapotranspiration. However, this amount and its seasonal dynamic may vary with the vegetation cover. Consequently, one might expect that any land use or climate changes could lead to the modification of the surface water and energy feedbacks, and, thus both the atmospheric and the regional water cycle. Finally, the sudanian region of West Africa is submitted to a 3% demographical increase per year, which induces a drastic expansion of crops areas. This study aims at quantifying the changes in evapotranspiration and sensible heat flux regimes caused by such a land use change under sudanian climate.The AMMA-CATCH observatory documents evapotranspiration flux in West Africa since 2007. A pluri-annual energy budget term of a clear forest and a cropland area are analysed. It is shown that sudanian forest evapo-transpirated always more than crop areas because of agricultural practice, which cleaned to bare the crops areas with bush fires and water availability for trees. Thus, during the dry season, the cultivated areas remain bare. At the same time, more than 1mm per day of evapotranspiration rate is measured above the forest area despite the lack of precipitations. Deep rooting systems allow the clear forest to get access to water from deep soil layers for transpiration throughout the dry season. During the rainy season, low but significant differences in evaporative fraction are also observed. These differences will lead to a large deficit of the water vapour that returns to the atmosphere, and, thus, will change significantly the continental water cycle when forests will be replaced by crops. In the future, agroforestry that combines local crops (yam, manioc, millet, etc.) and sparse trees could mitigate surface feedbacks. Finally, the selected trees could provide extra agricultural products taking benefit from deep water availability, but also strengthen social equilibrium between men and women.