By Mari Hansen 
You anticipate heat, silence, and the unique emptiness that makes people feel insignificant when standing at the edge of the Sahara. Mud is what you do not anticipate. or the sound of water flowing when it shouldn’t. But that’s precisely what happened in 2024, and NASA’s photos, which showed dry lake beds filling with water and satellite maps glowing green across a stretch of sand that hadn’t seen consistent rain in decades, had an almost hallucinogenic quality.
It wasn’t a drizzle. The Arba’at Dam, which was constructed specifically to handle the infrequent times when water did arrive, was unable to handle the situation in northeastern Sudan. Rainfall that, according to NASA estimates, amounted to about five years’ worth of precipitation arriving in a single month caused it to collapse.
| Category | Details |
|---|---|
| Location | Sahara Desert, North Africa (spanning 11 countries) |
| Size | Approximately 9.2 million sq km — largest hot desert on Earth |
| Annual Rainfall (Average) | Less than 25 mm per year in core desert zones |
| 2024 Rainfall Event | ~5 years’ worth of rain fell in northeastern Sudan in one month |
| Key Region Affected | Morocco, Sudan, Chad, Mali, Niger, Eritrea |
| Dam Collapse | Arba’at Dam, northeastern Sudan (2024) |
| Research Institution | University of Helsinki & University of Bristol |
| Study Published In | Nature Communications |
| Lead Researcher | Dr. Edward Armstrong, Climate Scientist |
| Historical Green Period | African Humid Period: ~8,700 to 4,300 years ago |
| People at Flood Risk (2024) | 4 million across 14 countries (World Food Programme) |
| Reference Website | NASA Earth Observatory |
South of the Atlas Mountains in Morocco, lakes formed in basins that residents in their fifties had never seen hold water. The Sahara “flooded for the first time in 50 years,” according to some somewhat heated headlines.” Although that was an exaggeration, it wasn’t wholly incorrect.
The fact that none of it happened by accident is what makes this stranger. By examining stalagmites inside Moroccan caves and reading the oxygen isotopes trapped inside like pages of an old diary, researchers at the University of Oxford had already begun literally delving into the history of the Sahara. They discovered that the Sahara was not a desert at all between 8,700 and 4,300 years ago.
It was green. It was traversed by rivers. It was home to Hippos. Neolithic societies cultivated the land, constructed villages, and seemingly had no idea that they were residing in an area that would eventually come to represent the ultimate representation of lifeless desolation. The African Humid Period, as scientists refer to it, was wet and real, and it is currently being researched with a renewed sense of urgency.
When his team published their findings in Nature Communications, Dr. Edward Armstrong, a climate scientist at the Universities of Helsinki and Bristol, stated clearly that the Sahara’s cyclical transition from desert to savannah is “one of the most remarkable environmental changes on the planet.” His team was one of the first to accurately model these humid periods, tracing their origin to something as vast and slow as Earth’s own wobble:
orbital precession, the 21,000-year cycle through which the planet tilts and shifts its relationship to the sun, changing how intensely the Northern Hemisphere bakes in summer and, consequently, how far north the West African Monsoon pushes each year. The Sahara receives rain when the monsoon extends far enough. The sand holds when it doesn’t.
Though scientists are cautious not to say so too confidently, it’s possible that the rainfall in 2024 was a glimpse of that ancient rhythm attempting to reassert itself. The Intertropical Convergence Zone, the atmospheric boundary where tropical and desert air collide, is already moving farther north than it usually does due to climate change. Climate researcher Karsten Haustein of Leipzig University told CNN that this boundary moves farther north as global temperatures rise.
The Northern Hemisphere, which contains more land than the Southern Hemisphere, tends to heat up more quickly, pushing that zone higher, according to Francesco Pausata, a professor of atmospheric science at the University of Quebec. As a result, some areas of the Sahara saw two to six times the usual amount of rainfall in 2024. It seems like positive news. It isn’t, or at least not in an obvious way.
The deep Sahara remained nearly unchanged when NASA examined vegetation data using the NDVI index, a measure of how green and alive a region is, calculated from orbit. This is the frustrating part that complicates every hopeful satellite image. Almost no dormant seeds can be found in sandy soil. The gradual geological negotiation between water and earth that creates vegetation cannot be triggered by a single month of rain, not even a dramatic, dam-breaking month.
The Sahel, the region of savannah that stretches along the southern edge of the Sahara, saw the majority of the greening that did take place because the soil there is richer and seeds have been waiting. The Sahel blossomed. For the most part, the desert did not.
Observing all of this, it seems as though the planet is doing something intricate and not fully intended. According to the World Food Programme, the same climatic change that filled dry lakes in Morocco also put 4 million people in 14 countries at risk of flooding. Other areas became drier as a result of the same atmospheric rearrangement that forced rain into the Sahara.
Because tropical weather systems were forming farther north and coming into contact with cooler air before they could fully develop—a result of the same ITCZ displacement—the Atlantic hurricane season was quieter than usual. Everything is connected to everything else, and these connections don’t always work out well.
It’s also important to note what Armstrong’s team discovered about the ice ages: the green periods in the Sahara did not occur during glacials, when the high latitudes of the Northern Hemisphere were covered by enormous ice sheets. The atmosphere was sufficiently cooled by those ice sheets to completely suppress the monsoon system.
According to co-author Miikka Tallavaara, the gate remained closed, leaving no green corridor or simple path for early humans or other species to travel between sub-Saharan and North Africa. Only when the ice receded and the temperature rose again did the gate open. The fact that we are currently melting ice quickly and possibly reopening conditions that once allowed life to spread, but doing so in a way that is also upsetting every other system we rely on, is a dark irony.
This is not a straightforward tale of nature healing. The Sahara is not getting better. It is reacting in quantifiable but poorly understood ways to orbital mechanics, changing monsoon boundaries, and the compounding pressure of a warming world.
According to co-author Paul Valdes, a professor of physical geography at Bristol, their updated climate model finally accurately depicts historical changes, which boosts scientists’ confidence in their capacity to predict future trends. That’s the cautious nature of science. It’s still unclear if the future will be a renaissance or a catastrophe, and it might appear to be both at once in the unsettling way that climate stories frequently do.