A shift in the diurnal timing and intensity of deep convection over the Congo Basin during the past 40 years

The Congo Basin, one of the three most convective regions in the world, has recently experienced a large-scale drying trend accompanied by an increase in thunderstorm activity. This study analyzes changes in the diurnal variations of cloudiness and deep convection from 1979 to 2019 over the Congo, evaluates their associations with trends in precipitation efficiency, and explores their possible connections to the observed decrease in precipitation. Analyses of GridSat-B1 and MODIS satellite datasets in conjunction with ERA5 reanalysis data show that cloud cover has decreased, and brightness temperature (Tb) has increased during the morning hours, while convective activity has increased and Tb has decreased during the afternoon hours, possibly due to the observed warming and drying trend over the Congo. The combined effects of decreasing clouds during the morning and the subsequent increasing convection during the afternoon have led to an amplification of the diurnal amplitude in Tb over the Congo. Our results also indicate a decrease in precipitation efficiency and an increase in cloud base height. Such changes may be attributable to the Congo drought as increased surface temperatures and decreased surface relative humidity would raise the lifted condensation level, and thus increase the cloud base height and decrease the precipitation efficiency. This positive-feedback mechanism may ultimately result in the observed decrease of precipitation at the surface, further accelerating the drying trend over the Congo. •The diurnal cycle of convection over the Congo Rainforest has shifted since 1979.•Clouds decreased in the morning, convective activity increased in the afternoon.•The convective temperature is reached earlier due to increased surface warming.•Precipitation efficiency decreased and cloud base height increased.•The observed changes may be attributable to the observed long-term drying trend.