Observation of Sensible and Latent Heat Fluxes Over a Mixed Savanna – Agricultural Catchment in the Semi-Arid Sudanian Savanna, Burkina Faso
Evaporation and the surface energy balance over two land cover types in Sudanian savanna were investigated in terms of their seasonal and interannual variability using four years of eddy covariance measurement (2009-2013). The observations demonstrate the strong controls on evaporation by vegetation through modification of the surface roughness, albedo, and available moisture related to seasonal variations in land cover and topography. Two characteristic land uses of semi-arid West Africa (Burkina Faso) were monitored: agricultural fields and gallery forest. The sites receive around 800 mm of rain most years, typically between the months of May and October, with up to approximately 20% being transferred to runoff. Seasonal variation in all components of the energy balance was found to be greater over the agricultural landscape, the total latent energy flux over the gallery forest was higher by approximately 30%, and the evaporative fraction was more dependent on soil moisture in the agricultural fields. According to the diurnal behavior of the evaporative fraction, we isolate constant periods that we compare with measures of cloudy sky, NDVI and soil moisture. We identify predictors of diurnal variation of the evaporative fraction according to land cover, which allows incorporation of remote sensing and satellite data. Improved understanding of the variability of fluxes over diverse land cover will allow us to improve the estimation of evaporation to the atmosphere over the entire watershed. Ongoing outreach projects accompany this research to integrate findings with local knowledge to improve resilience of small-scale rain fed agriculture.