Rare Extratropical Cyclone Floods Sahara Desert, Bringing Record Rainfall

"Although moderate rainfall occurs every summer in this region, what is unique this year is the involvement of an extratropical cyclone," said Moshe Armon, a lecturer at the Institute of Earth Sciences and the Hebrew University of Jerusalem. The phenomenon formed over the Atlantic Ocean and extended far south, drawing moisture from equatorial Africa to the northern Sahara, explains NASA, noting that "initial satellite analyses show rainfall totals ranging from several tens to over 200 millimeters in the affected areas, roughly equivalent to what the region receives in a year."

The exploitation of NASA’s IMERG (Integrated Multi-Satellite Retrievals for GPM) data has made it possible to obtain estimates of rainfall totals. This data constitutes one of the only options for systematically assessing rainfall in the Sahara over large areas, as rain gauges and ground-based radar stations are very rare.

"What is also fascinating is that the normally dry lakes of the Sahara are filling up due to this event," added Armon, who is closely monitoring the Sebkha el Melah salt lake in central Algeria, the subject of one of his most recent studies. To better understand the frequency of heavy rainfall episodes in this region, he and his colleagues analyzed two decades (2000-2021) of IMERG data. It emerges that only six events out of the hundreds that affected this area during this period led to the filling of the lake. Similarly, out of the 38,000 heavy rainfall episodes over the Sahara identified by the researchers, only a few were associated with an extratropical cyclone. They found that about 30% of them, like this one, occurred in the summer.