A lake materializes in the Sahara desert, offering a glimpse of Africa’s past

See Sebkha el Melah, an ephemeral lake in Algeria, seen from space.

The lake was formed after a cyclone lashed parts of North Africa in September, bringing huge amounts of rain to the Sahara desert. And now, he’s helping researchers study what the Sahara might have been like thousands of years ago—perhaps not a jungle, but a much wetter environment than it is today. Deserts generally receive less than four inches of rain a year, according to the National Science Foundation, indicating how important an ephemeral lake can be to life in the world’s largest non-polar desert.

You can see the Algeria region as it appeared in August and September 2024 below. There is an obvious dark green color difference. The rain arrived in early September and soaked parts of Morocco, Algeria, Tunisia and Libya.

The images were taken by the Operational Land Imager-2 (OLI-2) aboard NASA’s Landsat 9. As of last week, the lake was 33 percent full and covered an area of ​​74 square miles (191 square kilometers) at a depth of about 2.2 meters (7.2 feet), according to University researcher Moshe Armon Hebrew of Jerusalem, which reviewed satellite images of the lake.

Between 11,000 and 5,000 years ago, a wobble in Earth’s orbit turned the Sahara into a more lush environment than it is today. It was the African Wet Period, during which ancient humans painted animals and hunting scenes in caves and rocks across now dry areas of countries such as Egypt, Chad and Sudan. Lake levels in North Africa were much higher than today, and the region is very green. But some geologists argue that climatic conditions during this period could not have generated enough rain to fill the number of lakes that researchers estimate existed in what is now the Sahara.

“We propose a third possibility: that extreme rainfall events, like the one in September in the northwestern Sahara, may have been more frequent in the past,” Armon said in the Earth Observatory statement. “Given how long it takes for lakes to dry out, these events could have been common enough to keep lakes partially full for long periods, even years or decades, without frequent rainfall.”

Sebkha el Melah could be filled for years. When the lake’s salty bed filled in 2008, the water didn’t fully evaporate until 2012, according to a statement from NASA’s Earth Observatory. “If we don’t have more rain events,” Armon said, the lake “would take about a year to completely evaporate.”

Summer tends to be a wetter time for the Sahara. Of the 38,000 heavy precipitation events recorded in the desert, about 30 percent occurred during the summer, according to a previous release from the Earth Observatory.

Eyes from the sky are increasingly helping scientists monitor Earth’s water. In 2022, NASA and France’s CNES launched the Surface Water and Ocean Topography (SWOT) mission, a three-year undertaking that collects data on water volume and movement from orbit. Other spacecraft, such as NASA’s Deep Space Climate Observatory (DSCOVR), track atmospheric climate events.

Whether the lake remains filled for months or years, it serves as a reminder of how landscapes (and our understanding of them) can change with the planet’s changing climate.