The Sahara Desert, a symbol of barrenness and aridity, has witnessed a remarkable transformation. Satellite images from NASA’s Earth Observatory reveal a surprising burst of greenery across parts of Morocco, Algeria, Tunisia, and Libya. This unexpected flourish is the result of an extratropical cyclone that drenched the region on September 7 and 8, 2023.
The cyclone, an unusual occurrence for the Sahara, brought torrential rains, transforming the arid landscape into a temporary oasis. On September 10th, NASA’s Terra satellite captured images using the MODIS (Moderate Resolution Imaging Spectroradiometer), showcasing the dramatic impact of the rainfall. The false-color image revealed dark and light blue areas, indicating the presence of water runoff and floodwater. The depth of the water and the amount of suspended sediment influenced the shade of blue. In contrast, the same region appeared dry and barren in images taken on August 14th.
This dramatic shift in the desert’s landscape isn’t without consequences. Reports from France24 indicated that the torrential rains in Morocco led to devastating floods, claiming the lives of at least 11 people and leaving nine missing. The floods also destroyed 40 homes, damaged 93 roads, and disrupted electricity, water supply, and phone networks in several villages.
Scientists are studying this unprecedented event and its implications. Moshe Armon, a senior lecturer at the Institute of Earth Sciences and the Hebrew University of Jerusalem, explained that while some rainfall occurs in the Sahara during the summer, the involvement of an extratropical cyclone was unique. The cyclone, originating over the Atlantic Ocean, extended far southward, drawing moisture from equatorial Africa into the northern Sahara.
The impact of the cyclone was significant. According to preliminary satellite analysis, the affected areas received over 200 millimeters of rainfall, equivalent to the region’s annual average. This information was gathered using NASA’s IMERG (Integrated Multi-Satellite Retrievals for GPM) data, as ground-based rain gauges and radar stations are scarce in the region.
This heavy rainfall has filled several normally dry lakes in the Sahara, a further testament to the extraordinary nature of this event. Images reveal dark blue areas representing these filled lakes, including one in Morocco’s Iriqui National Park and Sebkha el Melah, a salt flat in central Algeria.
To understand the frequency of such heavy precipitation events, Prof. Armon and his colleagues analyzed two decades (2000–2021) of IMERG data. They discovered only six previous occurrences that led to lake filling, highlighting the rarity of this event. Their analysis of over 38,000 heavy precipitation events over the Sahara revealed that roughly 30 percent occurred during the summer.
This extraordinary rainfall event in the Sahara raises questions about the potential impact of climate change on desert ecosystems. While the long-term effects of this sudden burst of greenery remain to be seen, it serves as a reminder of the dynamic and often unpredictable nature of our planet’s climate.
