Processes behind the decrease in Congo Basin precipitation during the rainy seasons inferred from ERA-5 reanalysis

Abstract

The ongoing Congo Basin drying is linked to decreasing atmospheric water vapour. To comprehend the processes reducing precipitation, we analysed water and Moist Static Energy components, associated with heating sources using ERA5 reanalysis data over the period 1981–2022. The findings reveal that the precipitation deficit in the Congo Basin during March–April–May and September–October–November is primarily attributed to a decreasing trend in the vertical moisture advection anomaly induced by vertical velocity anomalies. Following this, a horizontal moisture advection anomaly induced by specific humidity anomalies plays a significant role. However, evaporation, horizontal moisture advection anomalies induced by wind anomalies, and vertical moisture advection anomalies induced by specific humidity anomalies do not appear to contribute significantly to the drying trend in the region. The horizontal propagation of MSE advection anomalies exhibits a similar pattern to that of moisture flux advection anomalies, both at different boundaries and within the basin itself. Conversely, the contribution of vertical advection of MSE anomalies remains weak. By integrating moisture and MSE budgets, we interpret the declining precipitation trend as a consequence of uplift driven by horizontal MSE advection. Furthermore, our analysis indicates a decreasing trend in the atmospheric heating source within the basin in association with reduced precipitation. This reduction could signify a decrease in moisture influx into the basin, thereby providing more explanations for the observed drying.