Rare storms create temporary lakes in the Sahara desert

New research highlights how certain storms can briefly transform parts of the Sahara into watery landscapes. Scientists have long been curious about occasional lakes in this desert, which is usually considered too dry to sustain these features for long.

The study involved meticulous analysis of rare flooding patterns in northwestern Algeria.

The research was led by Dr. Moshe Armon from the Institute of Earth Sciences at Hebrew University and Dr. Franziska Aemisegger from University of Bern, in collaboration with colleagues at University of Haifa and ETH Zurich.

The team investigated how strong rainfall events can temporarily fill a usually empty lake called Sebkha el Melah, challenging older ideas about how moisture used to reach the desert in the past.

What causes rare desert lakes?

Rain rarely falls in this region. The researchers wanted to see why short-lived lakes still appear now and then. They collected satellite data on heavy-precipitation events (HPEs) and mapped out when those storms coincided with significant increases in lake volume. 

“Results show that hundreds of HPEs occurred between 2000 and 2021, but only six LFEs (Lake-Filling Events) eventuated,” noted the study authors.

These episodes involved exceptionally intense storms that bypassed the usual rain shadow of the Atlas Mountains and carried oceanic moisture deep into the desert.

The scientists observed that extratropical cyclones along the Atlantic coast are an important driver. These weather patterns can pull in huge amounts of water vapor and direct it around the high terrain.

The moisture sometimes bounces through the Sahara, where it evaporates from falling raindrops that never reach the ground. The damp air then travels on, leading to a domino effect that amplifies water availability over time.

Intense storms fill the desert lake

Most rain systems lose intensity over the Atlas Mountains. When these storms are powerful enough and last for several days, the wind can navigate around higher ground before dropping rainfall into the normally parched basin.

Slower-moving cyclones can create heavier precipitation by allowing more moisture to flow into the desert.

Climate experts say such storms are more common during autumn and winter, though they occasionally happen in other seasons. The repeated appearance of these systems is crucial. A single day of light showers is not enough to fill a desert lake.

Multiple days of downpours, mixed with local convection and large-scale air lifting, seem necessary to generate the runoff that finally pools into Sebkha el Melah.

Future warming scenarios

The researchers also considered how rising temperatures might affect storm behavior. Some models predict an increase in moisture transport toward the Sahara under certain warming scenarios.

Any uptick in storm frequency or intensity could temporarily boost the region’s water resources. This does not promise permanent greenery, but it raises questions about how desert habitats and human activities might adapt if such precipitation patterns become more frequent.

Another surprise is that the rare flooding of Sebkha el Melah in September 2024 aligns with the same large-scale atmospheric patterns.

Landsat imagery from NASA Worldview confirmed that heavy rainfall again pushed Atlantic moisture far into the desert, mirroring what had been seen in previous lake-filling events.

Implications for long-term climate shifts

The researchers note that rainfall alone does not explain historical wet periods. They think massive storms, along with more frequent short-term flood events, may have shaped past moisture levels in the Sahara.

These findings add depth to the debate over how certain parts of the desert were once dotted with wetland habitats. The research also emphasizes the importance of understanding not just annual rainfall, but the specific kinds of storms likely to deliver enough water all at once.

The team calculated how each flood event translated into changes in the lake’s volume. Despite hundreds of storms over two decades, only the most powerful ones made a real difference.

This suggests that future projections about water availability should focus on both storm intensity and the pathways moisture takes, rather than looking solely at average rainfall statistics.

Grasping changes in harsh environments

The team applied meteorological reanalysis, satellite data, and field expertise to confirm that mixing science disciplines is necessary to grasp changes in harsh environments.

There is a sense of urgency when thinking about desert communities and the fragile ecosystems relying on sporadic water sources. Shifts in storm patterns could mean more frequent floods in certain pockets of the Sahara, offering hints of how water cycles might respond to a warming planet.

There is still an open question of whether these insights apply to other deserts with similar climates. The authors see value in investigating the synergy between large-scale atmospheric flows and local geographical features in regions where storms appear elusive.

The researchers also suggest that future climate models need higher resolution to capture these fleeting, powerful rainfall events to improve forecasts for desert hydrology.

The study is published in Hydrology and Earth System Sciences.

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