Hydroclimatic Analysis of the Unusual Wet Spell Observed in Senegal in July 2022

Résumé fourni par la source

In July 2022, Senegal experienced an exceptional wet spell characterized by widespread flooding and anomalously high rainfall intensity. This study investigates the multi-scale hydroclimatic mechanisms underlying this event, focusing on the combined roles of sea surface temperature (SST) anomalies, African Easterly Waves (AEWs), and intraseasonal variability associated with the Madden-Julian Oscillation (MJO). We combine satellite-based precipitation products (IMERG, CHIRPS, and TAMSAT), ERA5 reanalysis fields, and daily SST data (OISST v2) to diagnose the large-scale and mesoscale processes involved. AEWs and mesoscale convective systems (MCSs) are objectively tracked to quantify their contribution to rainfall variability. The results show that the event coincided with a pronounced tropical Atlantic SST dipole, characterized by anomalous warming in the North Tropical Atlantic and cooling along the equatorial Atlantic. This configuration enhanced the meridional SST gradient, strengthened the low-level monsoon flow, and increased moisture availability over West Africa. During the same period, total column water vapor exceeded 59 mm over Senegal, while a sequence of long-lived and coherently propagating AEWs was observed. Moreover, this event occurred during an active MJO phase (phases 8 - 1), which is known to favor enhanced convection over West Africa. The MJO likely acted as an intraseasonal modulator, reinforcing large-scale ascent and moisture convergence, thereby amplifying convection triggered by AEWs. The extreme rainfall arose from a compound mechanism involving persistent AEW activity, a moisture-rich background state, and favorable intraseasonal conditions linked to the MJO. These results underscore the role of multi-scale interactions in shaping extreme rainfall over west Africa and offer valuable insights for improving subseasonal forecasting and early warning systems.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.