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Stormy rains in the Sahara offer clues to past and future climate changes

A new study recently in Hydrology and Earth System Sciences, provides new insights into the meteorological processes responsible for the filling of a normally dry lake in the northwestern Sahara. The research offers a fresh perspective on past climate variations and suggests we can learn from past flooding of the lake on ongoing climate change and future water resources in the desert.

The research was supervised by Dr. Moshe Armon from the Institute of Earth Sciences at Hebrew University and Dr. Franziska Aemisegger from University of Bern, in collaboration with Dr. Elad Dente from University of Haifa, led by their student Joëlle Rieder at ETH Zurich.

The Sahara Desert, one of the driest places on Earth, has not always been as arid as it is today. Prehistoric evidence of wetlands in the Sahara points to wetter periods in the past, but scientists have long debated the sources of moisture responsible for these ancient water bodies. The study examines how the currently dry Sebkha El-Melah lake in western Algeria is occasionally filled with water, shedding light on the extreme storm events required to sustain such bodies of water.

The study found that between 2000 and 2021, hundreds of powerful rainstorms were recorded in the lake's drainage basin, yet only six instances led to substantial lake-filling events. These lake-filling events were driven by precipitation systems originating from the Atlantic Ocean, rather than equatorial sources as previously believed.

The moisture transport process involves the interaction of extratropical cyclones near the North African Atlantic coast with upper-level atmospheric patterns, creating conditions favorable for heavy precipitation events. A crucial factor in these events is the recycling-domino effect, in which moisture is progressively transported and enhanced over the Sahara before reaching the lake's drainage basin.

The team found that the stationarity of weather systems, lasting typically three days, contributes significantly to the occurrence of lake-filling events.

This research challenges conventional theories suggesting that prehistoric lakes in the Sahara were primarily filled by monsoonal rains from the south. Instead, it highlights the role of Atlantic-origin storms, which deliver oceanic moisture into the desert, bypassing the Atlas Mountains. These findings have important implications for understanding past climate conditions and predicting future hydrological changes in desert environments.

The study further suggests that potential future climate shifts—driven by global warming—have the potential to fill Saharan lakes not only due to increased rainfall, but also because of changes in the frequency of extreme rainstorms. This could reshape water availability in the region, with significant consequences for ecosystems and human settlements.

By integrating climate science, meteorology, remote sensing, and hydrology, this research bridges a critical knowledge gap and provides a framework for future studies on Sahara Desert hydrology and climate dynamics.