Changes in the tropical rainfall seasonal cycle dominated by mesoscale convective systems

Abstract

Global warming is reorganizing atmospheric circulation and hydroclimate, and tropical rainfall is a key manifestation of this response. Yet how these large-scale changes are translated into the tropical rainfall seasonal cycle remains uncertain because organized convection, which produces a large fraction of tropical rainfall and often occurs in mesoscale convective systems, is poorly represented in conventional climate models. Here we use decade-long global simulations with a high-resolution Earth system model coupled to a multiscale modelling framework that explicitly represents deep convection to quantify the role of mesoscale convective systems in future rainfall seasonality. We find that mesoscale convective systems would dominate the future changes in both the amplitude and phase of tropical precipitation seasonal cycle. Under a high-emission scenario, the seasonal cycle of precipitation from mesoscale convective systems is amplified by 38–45% and delayed by 10–15 days, exceeding the corresponding changes in mean tropical precipitation. The delay arises from fewer early season mesoscale convective systems associated with slower seasonal migration of the Hadley cell, whereas amplification is driven mainly by increased rainfall intensity within these systems. These results indicate that organized convection is a major pathway through which warming reshapes tropical rainfall seasonality, affecting the timing and intensity of hydroclimate risks. High-resolution simulations project that the seasonal cycle of precipitation from mesoscale convective systems will intensify by 38–45% and be delayed by 10–15 days under high emissions, driving future changes in tropical rainfall seasonality.