Evaporation (sometimes referred to as ‘evapotranspiration’) is the transfer of water vapour from the land surface into the atmosphere. Evaporation drives weather patterns, affecting cloud formation, convection and rainfall. In the Congo Basin, evaporation from the tropical rainforest to the north and from the deciduous savannah to the south is believed to provide up to 50% of the moisture that is returned to the surface as rainfall. Understanding the processes responsible for the annual cycle of evaporation is desirable, as these processes are likely to have important consequences for the seasonal differences in rainfall amount and distribution across the basin. However, the processes controlling this seasonality have been understudied, owing to a lack of available observational data from flux towers.
In his DPhil project, David aims to evaluate global climate model, reanalysis and satellite data to determine, in the absence of in situ observations, the most likely set of dynamics which control the seasonality of Congo Basin evaporation. His first publication in Journal of Geophysical Research: Atmospheres examined the credibility of the evaporation produced in the Congo Basin by eleven global climate models. He found that the models which produce evaporation realistically against reliable reference data consistently produce less evaporation at the peak of the second rainy season (November) than the peak of the first (March) on the basin-wide average, because the models release less transpiration from the vegetation. In follow up work, David aims to continue exploring the climatology of Congo Basin evaporation using reanalysis and satellite data, in order to move towards a more complete understanding of why the annual cycle of evaporation behaves as it does.