Impact of the MJO on the extreme precipitations in the Mexican Valley

This research aims to determine how the Madden-Julian oscillation (MJO) influences extreme summer precipitation events in the Metropolitan Area of the Mexican Valley (MAMV). Using the Real-time Multivariate MJO Index (RMM), we found a higher frequency of days with extreme events during phases 1 and 2 of the MJO (wet phases), with the lowest occurrence during phases 6, 7, and 8 (dry phases). These frequencies are associated with positive (negative) humidity anomalies in the whole atmospheric column of the study region during the wet (dry) phases. The interaction of a humid flow from the Caribbean Sea with the mountain systems of the region plays a fundamental role in the occurrence of deep convection. Also, the formation of mesoscale convective systems in the central region of the Mexican territory contributes to the moisture content in the Mexican Valley. We used the Dynamic Recycling Model to quantify the relative contributions of different source regions to the atmospheric humidity in MAMV. We found that the greatest contributions to the humidity anomalies are from the Caribbean Sea and Central Mexico during the wet phases of the MJO. During the remaining phases, we observe a weakening of the humid flow from the east as the Caribbean low-level jet intensifies. Additionally, during phases 7 and 8, the mountainous systems that limit the MAMV constitute natural barriers to the flow of humidity that tends to be predominantly from the eastern Pacific. The MAMV is highly vulnerable to extreme precipitation events and their effects, such as pluvial floods and landslides. Therefore, studying the phenomena that modulate these extreme events is essential to improve their predictability and perform better risk management.