Abstract 214

Abstract ID: 214

Multiple tropical waves occurrence drive extreme precipitation events in the central Sahel

Lead Author: Philippe Peyrille
CNRM, Meteo-France, France

Keywords: extreme, precipitation, Sahel, tropical, waves

Abstract: Atmospheric conditions leading to extreme precipitation events (EPE) in the Central Sahel are examined at subseasonal timescale with a focus on tropical waves. EPE are first detected using a dense rain-gauge network over Burkina Faso, which corresponds to a significant part of the central Sahel. A composite analysis reveals that a high humidity associated with a large-scale humid envelope, anomalous divergence in the upper troposphere and a strong layer-averaged relative vorticity are key elements at play in the occurrence of an EPE. The multiple occurrence of tropical waves is found to be a key driver of such an atmospheric environment. The occurrence of very intense regional synoptic disturbance – so-called African Easterly Waves – with a marked vorticity and humidity anomaly together with a larger-scale Equatorial Rossby wave is the dominant factor in most of the EPE cases. The occurrence of multiple tropical waves in their convectively phases is a key feature of EPE, not found for less intense precipitation events, that provide a favorable preconditioning for an intense EPEs that point to an increased predictability in Sahel and potentially in other semi-arid regions. An example of operational use of this scenario will we shown on the 2022 monsoon season.

Romain Roehrig (CNRM, Meteo-France)
Sidiki Sanogo (IPSL)