Increased in Dry Season Length Over the Congo

The duration of both the wet and dry seasons are crucial to soil water content and vegetation distribution, especially over tropical forests experiencing complicated seasonality (unimodal or bimodal) variations under climate change. Longer dry season would make forests expose to high risk of wild fires, shrink the edges of the forest, and alter the vegetation type. Here we present observational evidences for a longer boreal summer dry season length (DSL) over the Congo Basin since 1980s based on analyses of three long-term observational precipitation datasets and two satellite-derived vegetation products. The increase of DSL, particularly in the central and southern Congo, is primarily owing to an advance of dry season onset ( DSO) with decreased precipitation in the transitional season (April-June, AMJ). It is accompanied by the delayed end of dry season observed from the two independent satellite products. The increased DSL would affect the growth and photosynthetic activities of the canopy through changing incoming solar radiation fluxes and moisture contents. A shrink of the southern edge of the ITCZ and a weaker convergence in the center of the ITCZ seem to cause the decreased precipitation in AMJ and the advanced DSO in boreal summer. Further work is needed to better understand the mechanisms of variations of the dry season as precipitation over the equatorial Africa is also influenced by other factors such as upper level jets, tropical SSTs and anthropogenic forcing.