Synoptic drivers of the August 2024 record-breaking rainfall in the Chadian Sahara: Dynamics, thermodynamics, and socio-economic consequences

Abstract. This study examines the atmospheric mechanisms behind the extreme rainfall event of August 2024 in the northern Chad, and their devastating socio-economic impacts. Analysis of the hydro-climatic regime over the region reveals a major structural transition marked by a statistical tipping point in 2003, shifting from historical aridity to a phase of intensified rainfall that culminated in the record high of August 2024. Our analysis of lower-tropospheric convergence, specific humidity, vertical velocity (ω), and moist static energy (MSE) reveals a major shift from the typical West African monsoon regime. In August 2024, the Intertropical Front (ITF) shifted abnormally northward, reaching 20–22° N, which allows moist moisture air to penetrate deep into the Saharan zone. This shift was driven by strengthened convergence at 850 hPa and a significant increase in low-level humidity. Furthermore, negative ω anomalies throughout the troposphere indicate a northward extension of the monsoon's upward branch. Strong positive MSE anomalies over desert regions further highlight a thermodynamic enrichment of the atmospheric column. Together, these signals point to a highly effective dynamic-thermodynamic coupling that fueled intense convective systems. Ultimately, the synchronization between these atmospheric condition and the synoptic forcing of African easterly waves generated local rainfall anomalies exceeding 100 %, redefining the hydrological balance of the Lake Chad basin between aquifer recharge and increased risks of flash flooding. This hydro-climatic shift had immediate and devastating socio-economic impacts: the resulting flooding affected nearly 20,000 people across four desert provinces in Chad. In Tibesti alone, sixty lives were lost due to drowning or building collapses, alongside significant losses of livestock and infrastructure.