DrY Season in northern Central Africa: variabiliTy, evoluTion and Impacts on forests – DYSCATTI

In the late Holocene, the forests of the northern margins of Central Africa disappeared. Recently, a decline in their greenness has been observed. While the climatic origin of the late Holocene forest crisis is disputed, the question of a further destabilisation of these forests as result of climate change is being raised. Equatorial forest climates are often perceived as being free of dry seasons (DS), and the causes of forests’ decline are mainly sought in disruptions of the rainy seasons. However, 2 weather stations set-up in the north of the Republic of Congo in 2016 show that the boreal winter season is characterized by both rainfall and atmospheric dryness, with spells of dry air lasting up to 3 weeks. Little is known about the winter boreal DS of the northern margins of the Central African forests although recent studies suggest that the dryness of the DS is a key determinant of both the past and current extent, and functioning of African forest ecosystems. Therefore the main objective of DYSCATTI is to study it on a Holocene-Anthropocene continuum in order to understand its variability and evolution, and to shed light on its potential impact on these forests. Thanks to the synergistic analysis of original in-situ meteorological data, and transient climatic simulations with dynamic vegetation for the past 6 kyr, plus reanalyses and CMIP6 simulations, we will document the intraseasonal to multi-centennial variability of the DS, to gain insights about forcings and mechanisms that shape extreme DS. Transient climatic simulations and satellite estimates will also be used to assess, respectively, the slow and fast responses of forests to the DS variability, i.e. changes in their spatial extent over the last 6 kyr, and year to year changes in carbon fluxes, biomass, … over the last decades.