A study on Sebkha el Melah lake in Algeria links the filling of ancient Sahara lakes to weather systems in Morocco, specifically Atlantic-origin storms. The research highlights that heavy rainfall events, rather than a general increase in precipitation, are key to lake-filling episodes. The Sahara Desert has not always been dry and arid. Researchers believe that in the past, it may have been wetter and greener, with even lakes. To understand this wetter past, scientists have been studying paleo-lakes in Algeria and weather data from the western coast of Morocco. In a study published earlier in March in Hydrology and Earth System Sciences, researchers from Switzerland and Israel sought to link present-day hydrological events with past climate patterns in the Sahara. The researchers focused on Sebkha el Melah lake in northwestern Algeria, an ancient lake that serves as evidence of the Sahara's wetter past. The study aims to learn more about when and why lakes in the Sahara fill up, using this lake as a key example. To achieve this, the study examined heavy precipitation events (HPEs) and lake-filling episodes (LFEs). HPEs occur when a large amount of rain falls, and LFEs refer to periods when lakes fill with water. The researchers used satellite data to track water levels in the lake and combined this with weather data to understand the conditions leading to heavy rain and lake filling. Additionally, they used data from weather models (called "weather reanalysis") to determine the source of moisture in the rain and how weather systems develop. Cyclones near the North African Atlantic coast The findings link the filling of ancient lakes to weather conditions in Morocco. They have linked intense rainfall originating from the Atlantic Ocean to modern lake-filling events in the northwestern Sahara. Specifically, the researchers identified low-level cyclones—large, rotating storm systems forming off the coast Morocco—as a key factor. These cyclones, along with upper-level atmospheric features and moisture from the tropics, move through Morocco into Algeria, creating favorable conditions for filling the lake during rainfall events. The findings suggest that moisture transport involves the interaction of extratropical cyclones near the North African Atlantic coast with upper-level atmospheric patterns, creating conditions conducive to heavy rainfall. A crucial element in these events is the «recycling domino effect», where moisture is progressively transported and enhanced over the Sahara before reaching the lake's drainage basin. The study concludes that the filling of lakes in the Sahara is more closely related to the intensity and frequency of specific weather events, like heavy rainfall, than to a simple increase in overall rainfall.
