Dynamics of water vapor and energy exchanges above two contrasting Sudanian climate ecosystems in Northern Benin (West Africa)

Natural ecosystems in sub-Saharan Africa are experiencing intense changes that will probably modify land surface feedbacks and consequently the regional climate. In this study, we have analyzed water vapor (Q(LE)) and sensible heat (Q(H)) fluxes over a woodland (Bellefoungou, BE) and a cultivated area (Nalohou, NA) in the Sudanian climate of Northern Benin, using 2years (from July 2008 to June 2010) of eddy covariance measurements. The evaporative fraction (EF) response to environmental and surface variables was investigated at seasonal scale. Soil moisture was found to be the main environmental factor controlling energy partitioning. During the wet seasons, EF was rather stable with an average of 0.750.07 over the woodland and 0.700.025 over the cultivated area. This means that 70-75% of the available energy was changed into actual evapotranspiration during the investigated wet seasons depending on the vegetation type. The cumulative annual actual evapotranspiration (AET) varied between 73050mmyr(-1) at the NA site and 104070mmyr(-1) at the BE site. With similar weather conditions at the two sites, the BE site showed 30% higher AET values than the NA site. The sensible heat flux Q(H) at the cultivated site was always higher than that of the woodland site, but observed differences were much less than those of Q(LE). In a land surface conversion context, these differences are expected to impact both atmospheric dynamics and the hydrological cycle. Key Points At least 70% of the available energy was changed into actual evapotranspiration during wet seasons Soil moisture was found to be the main factor controlling energy partitioning The annual cumulative AET measured was 30% higher over the woodland than over the cultivated are