Convection‐Permitting Projections of Low‐Level Jets and Mesoscale Convective Systems in South America

Abstract Anthropogenic warming is expected to substantially modify the hydroclimate of South America, a region in which low‐level jets (LLJs) and mesoscale convective systems (MCSs) are key components of moisture transport and precipitation. However, the responses of these systems to future climate change, including the relative roles of thermodynamic and dynamic forcing, remain poorly understood. Using convection‐permitting model projections under a climate warming of approximately 3°C above preindustrial levels, this study examines future changes in the characteristics of LLJs and MCSs. The results reveal a widespread thermodynamic intensification of MCS precipitation, with maximum rainfall rates surging at magnitudes consistent with thermodynamic expectations. However, the structural evolution of MCSs exhibits a sharp dynamic bifurcation between the tropics and subtropics. In Southeastern South America, the strengthening of the background northerly flow enhances vertical wind shear during Central and Andes LLJ events. This kinematic support facilitates the upscale growth of MCSs into larger, longer‐lived complexes, elevating the potential for high‐volume hydrometeorological extremes. Conversely, the projected circulation anomaly across the western Amazon basin weakens the Northern LLJs, reducing the dynamic organization of historical squall lines and favoring a transition toward widespread, thermodynamically driven, loosely organized convective clusters. These regional shifts are consistent with a stationary Rossby wave train resembling the Pacific‐South American pattern, which enhances meridional moisture transport into the subtropics. These findings highlight a transition toward a complex hydrometeorological hazard profile, in which future extremes are defined not merely by total rainfall, but by regime‐specific changes in storm morphology, duration, and peak intensity.