Representation of Dynamic and Thermodynamic Processes During Heavy Rainfall Conditions in the Congo Basin in CMIP6 Models

Abstract

Accurate representation of water vapour fluxes during extreme precipitation events by climate models is essential if we want to trust their future projections. Here, we examine the ability of the models from the Coupled Model Intercomparison Project of phase 6 (CMIP6) to represent the components of moisture fluxes, moisture static energy (MSE) budget, and atmospheric heating sources associated with extreme precipitation seasons in the Congo Basin. Our results reveal that the majority of CMIP6 models are in agreement with ERA5 in indicating that positive seasonal precipitation anomalies in the Congo Basin are controlled by vertical moisture advection induced by vertical velocity anomalies in both March–May (MAM) and September–November (SON) seasons. Analysis of the MSE balance shows that in MAM, vertical MSE advection induced by vertical motion is dominated in the southern part of the domain by horizontal MSE advection induced by MSE anomalies, while in the north, changes in the energy balance control vertical instability. However, it is important to emphasize that the positive anomalies of the horizontal MSE advection induced by the MSE anomalies are offset by the negative anomalies of the residual term, which weakens the atmospheric instability. In SON, there are significant contributions from the net energy balance and the residual term, mainly to the west of the Congo Basin and along the Gulf of Guinea. Conversely, the MSE budget is more noisy in both ERA5 and CMIP6 models and has an important residual term that suggests the linearization used here is insufficient to fully represent the budget. The investigation of the integrated atmospheric heating reveals that ERA5 simulates high values, especially in regions where heavy precipitation is recorded. Analysis of the CMIP6 models, including the ensemble mean model, similarly simulates high heating source values in extreme precipitation areas throughout the Congo Basin. The results of this study highlight the ability of the CMIP6 models to simulate the moisture and heating source balance during periods of extreme precipitation in the Congo Basin.