Tag Archives: sahara

It’s greener than you thought: New tree count in Sahara shows surprising results

Using satellite imagery and a new AI algorithm, scientists were able to perform the first tree count in the Sahara area. Normally, it’s nigh impossible to count individual trees over a large region, but the method represents an important advance that could be used in other areas to answer this question.

The number of trees in the Western Sahara area exceeds 1.8 billion, the analysis shows.

Trees and shrubs play a crucial role in arid areas. They offer shelter and resources for local wildlife, and protect the environment from degradation (such as erosion). But assessing and monitoring the number of trees in these remote areas is no easy feat.

Separating individual trees from their canopy was thought to be impossible. But Martin Brandt and colleagues weren’t discouraged. They used high-resolution remote sensing data along with satellite images and then applied an artificial intelligence pattern recognition algorithm.

It’s the first time anything like this has ever been done.

“Previous assessments were estimations or extrapolations of the canopy area without any information on the numbers, here we have a wall-to-wall identification of each tree and shrub,” Brandt, associate professor at the University of Copenhagen tells ZME Science.

According to the study, the area comprising of Western Sahara, the Sahel, and Sudanian zone features an impressive number of trees. Even as the study only focused on trees with a crown size greater than 3m², they found that isolated trees cover about 1.3 million km² (an area 6 times larger than the UK). It’s hard to draw any immediate conclusions about what this means for Western Africa, but what really stands out is the method itself, which highlights the potential to create a global tree inventory.

Large-scale tree mapping. Image credits: Brandt et al..

“We cannot really say that the environment is in a better state than we thought, because local studies have shown that there are trees, so this is not a secret, but now we have a tool to precisely map the number and crown area of each tree, which certainly will help to better understand the environment and carbon cycle of dry areas,” Brandt adds.

The method can be applied in other settings, Brandt notes. Anywhere you have satellite data with 0.5 meters resolution, it could be applied — although the algorithm does need to be retrained for every particular objective.

“Generally, deep learning works as follows: we show the algorithm how a tree looks, and it will search the satellite images and mark the tree crowns as it has learned it from the training. That works surely with everything that we can identify with our eyes, like houses or cars, or even cows. The requirement is satellite imagery which is normally very expensive.”

Niall Hanan is a community and ecosystem ecologist who published a commentary article on the study, is also excited about the prospects.

“I was particularly interested in the study by Brandt and colleagues, because it provides a clear demonstration of our growing ability to measure terrestrial vegetation at the scale of individual trees. They mapped individual trees in some 1.3 M km² of West Africa, but the study shows the potential for mapping individual trees worldwide,” Hanan tells ZME Science.

This represents an important advance because unlike previous generic descriptions that analyzed “tree cover”, this can also provide information on tree density, canopy size, and the number and location of individual trees. This could be transformative for how we model and manage global ecosystems, Hanan notes. But he’s not so sure about applying the approach to different ecosystems just yet.

Before we can do that, we need better, cheaper access to satellite data, as well as more efficient algorithms. But the groundwork has been laid down.

“The deep learning approach used by Brandt and colleagues won‘t be easy to apply at global scales, in part because of the data and computational size of the task, but more particularly because of the overhead in terms of providing sufficient training data. Further advances in efficient deep learning methods are probably needed to make global mapping of trees feasible, but this study demonstrates the possibility.”

Journal Reference: Brand et al, An unexpectedly large count of trees in the West African Sahara and Sahel. Nature, 14 october 2020. DOI : 10.1038/s41586-020-2824-5

“Godzilla” dust cloud races from the Sahara to the US

Every year during summer, the wind carries large plumes of desert dust particles from the Sahara Desert in Africa across the Atlantic Ocean.

Now, thanks to satellite data from the European Space Agency (ESA), we can see in incredible detail the extent of this year’s dust plume — it was an unusually large, “Godzilla” plume.

Credit ESA

The Saharan dust storm, also known as the Saharan Air Layer, typically forms between late spring and early autumn, peaking in late June to mid-August. Dust particles from the African desert are swept up into the dry air by strong winds and thunderstorms. The dust can then float for days or even weeks on end.

This phenomenon happens every year but the plume now registered is described as unusual due to its size and the distance travelled. Researchers at the National Oceanic and Atmospheric Administration (NOAA) estimated that the dust plume is between 60 to 70% dustier than average, making it the most massive since records began 20 years ago.

The ESA created an animation that shows the spread of particles from the Saharan dust plume moving westward from June 1 to June 26 this year. The data, captured by the ESA’s Copernicus Sentinel and Aeolus satellites, shows the dust plume on its great journey, around 1.8 to 3.7 miles above the ground.

Normally, Saharan dust plumes disperse in the atmosphere and sink into the Atlantic before reaching the Americas, but this wasn’t the case this year, according to satellite data. The dense concentration of dust traveled about 8,000 kilometers and can be seen arriving close to the Caribbean and the southern United States.

The ESA’s Copernicus Sentinel-5P satellite, launched in October 2017, maps air pollutants using an instrument that measures the radiation of different wavelengths. Meanwhile, the Aeolus satellite, launched by the ESA in August 2018, tracks wind speed and direction across the globe.

Aeolus is the first satellite to acquire profiles of Earth’s wind on a global scale the satellite also delivers information about the vertical distribution of aerosol and cloud layers. This combination of data allows scientists to improve their understanding of the Saharan Air Layer, and allows forecasters to provide better air quality predictions.

While it can be a threat to our health, triggering air quality alerts, the dust travelling from the Saharan Desert is also very important for ecosystems. Dust is a key source of nutrients for the tiny algae known as phytoplankton that live drift on the surface of the ocean. Minerals from the dust fall in the ocean, triggering blooms of the algae to form on the surface of the ocean – providing food to marine life.

At the same time, the dust is also very important for life in the Amazon region, replenishing nutrients in the rainforest soils which otherwise would be depleted due to the frequent rain in the region. The dusty air layers have also been found to limit the development of hurricanes and storms in the Pacific.

More than a billion people could live in Sahara-like unbearable heat within 50 years

Credit: Pixabay.

We like to think of ourselves as a highly adaptive species, which is true to a degree. However, it is also true that humans have historically preferred to settle in habitats where the temperature is just right for both comfort and food production. But rapidly accelerating climate change is disrupting many regions that momentarily enjoy equilibrium, potentially threatening the livelihoods of billions of people.

Hotter than the Sahara for more than a billion people by mid-century

For many creatures, their habitat is predicated on temperature — this is also one of the reasons why abrupt climate change is so dangerous.

Warmer water temperatures cause declines in the populations of trout, salmon, and many other species that require cold water to survive.

Many species take their cues about when to migrate, flower, nest, or mate from seasonal changes in temperature, precipitation, and daylight. Climate change is confusing those signals and forcing wildlife to alter their behavior.

Professor Marten Scheffer of Wageningen University, Netherlands, and colleagues investigated the effects of climate change projected for the future from a curious angle. Instead of calculating the economic impact or going too much into the physics of climate change like other climate models, the researchers wanted to see how rising temperatures will affect human habitats.

According to the researchers, the vast majority of the population lives in regions where the average annual temperature is between 6°C (43°F) and 28°C (82°F). It has been this way for the last 6,000 years or so.

By the end of the century, global average temperatures are expected to increase by an additional 3°C. However, that’s the average. Some terrestrial regions might heat by as much as 7.5°C, which could make certain habitats unbearably hot.

The modeling work performed by the researchers, which was described in the journal Proceedings of the National Academy of Sciences, suggests that a third of the world’s population will live in areas that are as hot as the Sahara within the next 50 years under the worst-case scenario.

In the best-case scenario (3°C of warming by the end of the century), 1.2 billion people will live outside their “climate niche”, experiencing average annual temperatures over 29°C (84°F).

The worst affected countries will be India, Nigeria, Pakistan, Indonesia, Sudan, Niger, Philippines, Bangladesh, Burkina Faso, and Thailand, in this order.

Some of these effects can be mitigated by technology, particularly air conditioning. We’ve seen this work in seemingly inhospitable places such as urban UAE or Saudi Arabia. However, air conditioning is a luxury that the vast majority of people cannot afford, not to mention the fact that the energy required to cool homes and office spaces drives even more global heating.

Instead, what will likely end up happening is mass migration towards cooler regions. Additionally, regions that will experience temperatures past historically comfortable levels will also suffer significant impairments to their food supply, driving even more migration possibly conflict.

“I think it is fair to say that average temperatures over 29C are unliveable. You’d have to move or adapt. But there are limits to adaptation. If you have enough money and energy, you can use air conditioning and fly in food and then you might be OK. But that is not the case for most people,” Prof Marten Scheffer of Wageningen University told The Guardian.

The coronavirus pandemic has caused an unprecedented dip in greenhouse gas emissions that hasn’t been seen since World War II. However, emissions are bound to rebound and return to their usual upward trend once restrictions lift for good.

A U.N. report issued in 2019 found that global emissions would have to drop by 7.6% year-to-year, on average, if we’re to stand a chance at limiting global temperature rise to 1.5 degrees Celsius.

Crises like the coronavirus show just how fragile our economies and livelihoods can be in the face of global calamities. But in contrast to a pandemic, global heating is slow to develop, which gives the impression that things aren’t that bad — not yet at least.

These findings might, hopefully, motivate policymakers to stick to their Paris Agreement pledges, otherwise billions may find themselves living in misery. 

Sahara desert.

Clean energy could make the Sahara green

Installing solar and wind power in the Sahara would have benefits for both the region and the world’s grids, a new paper concludes.

Sahara desert.

Image via Pixabay.

The Sahara may be a deserted place, but according to the new study, green energy could also help the desert itself become greener: filling in all that empty space with solar and wind farms would help liven up the place — all while supplying ample green energy. Researchers from the University of Illinois at Urbana-Champaign (UI) found that such installations would increase local precipitation levels, which in turn would lead to increased vegetation.

The paper also reports that such power plants would also increase local temperatures under current conditions. However, this effect would likely be ‘very different’ in the field, due to the shift in vegetation patterns associated with changes in precipitation.

Greening Sahara

“Previous modeling studies have shown that large-scale wind and solar farms can produce significant climate change at continental scales,” says lead author Yan Li, a postdoctoral researcher in natural resources and environmental sciences at the UI.

“But the lack of vegetation feedbacks could make the modeled climate impacts very different from their actual behavior.

The team focused on the Sahara for several reasons: for starters, it’s the largest desert in the world. It’s also sparsely inhabited, and “highly sensitive to land changes”, Li explains. Furthermore, its geographical position — in Africa, but fairly close to both Europe and the Middle East — would also make it an ideal place to build plants that cater to these areas’ large (and growing) energy markets.

Li and colleagues simulated the effects of wind and solar farms covering in excess of 9 million square kilometers (roughly 3.5 million sq miles). On average, the simulated wind plants would churn out 3 terawatts, and solar ones 79 terawatts, of electrical power per year. Needless to say, that is a lot of powerplants: global energy demand in 2017 totaled about 18 terawatts, making the team’s scenario a tad overkill.

But what the team really wanted to see was what environmental effects solar and wind installations would have on the desert — as such, they needed to model the plants on a huge scale.

Their work revealed that wind farms do indeed increase near-surface air temperatures. Changes in minimum temperatures were greater than those seen in maximum temperatures, the team adds — i.e. wind farms increase minimum temperatures more than maximum ones.

“The greater nighttime warming takes place because wind turbines can enhance the vertical mixing and bring down warmer air from above,” the authors wrote.

Precipitation levels also increased by as much as 0.25 millimeters per day on average in regions with wind farm installations. The Sahel region saw the largest increases in average rainfall — 1.12 millimeters per day where wind farms were present.

Sahara changes.

Impacts of wind and solar farms in the Sahara on mean near-surface air temperature (in Kelvin) and precipitation (millimeters per day).
Image credits Li // Nature.

Overall, the increase in precipitation levels was double “that seen in the control experiments,” Li said. Such levels of precipitation would, in turn, lead to increased vegetation cover, he adds, “creating a positive feedback loop”.

“The rainfall increase is a consequence of complex land-atmosphere interactions that occur because solar panels and wind turbines create rougher and darker land surfaces,” says study co-author Eugenia Kalnay from the University of Maryland.

Solar farms had a similar effect on temperature and precipitation. Unlike the wind farms, solar installations had almost no effect on wind speeds.

Put together, the changes seen in the team’s model could have a very positive effect on the economic and social well-being in the Sahara, Sahel, Middle East, and other nearby regions, the team writes. The combination of clean (and cheaper) energy and increased rainfall and vegetation would also help boost local agriculture, they add.

The paper “Climate model shows large-scale wind and solar farms in the Sahara increase rain and vegetation” has been published in the journal Nature.

The Sahara desert expanded by 10% in the last century

Tadrart Acacus desert in western Libya, part of the Sahara. Credit: Wikimedia Commons.

Tadrart Acacus desert in western Libya, part of the Sahara. Credit: Wikimedia Commons.

In almost a hundred years, the Sahara Desert has expanded by 10%, according to a new study. The authors say that both natural climate cycles and human-induced climate change have contributed to this worrisome expansion threatening the livelihoods of agricultural-based communities.

A continent turning to sand and dust

The Sahara is the largest hot desert in the world, and the third largest desert after Antarctica and the Arctic. Scientists typically classify a region as a desert if it receives less than 100 millimeters (4 in.) of rainfall annually.

This is not the first study to report an expansion of the Sahara, and therefore the report in and of itself is not that surprising. However, the new research carried out at the University of Maryland is unique because it analyzed trends to infer changes in the desert expanse on the century timescale.

The researchers learned by studying the rainfall data recorded throughout Africa from 1920 to 2013 that the Sahara, which occupies much of North Africa, expanded by 10%. You might not notice it by looking at a Mercator world map (notorious for its distortions), but the Sahara is actually as large as the contiguous United States.

“Our results are specific to the Sahara, but they likely have implications for the world’s other deserts,” said Sumant Nigam, a professor of atmospheric and oceanic science at UMD and the senior author of the study.

According to Nigam and colleagues, the Atlantic Multidecadal Oscillation (AMO) is one of the primary drivers of the Sahara’s rapid expansion. This is a climate cycle that affects the sea surface temperature (SST) of the North Atlantic Ocean with an estimated period of 60-80 years. There is also seasonal variability: the desert expands in the dry winter and contracts during the wetter summer, with the most notable differences occurring along the northern and southern boundaries of the Sahara.

Between the barren Sahara and the fertile savannas further south lies a semi-arid transition region called the Sahel. When the Sahara expands, the Sahel inevitably contracts, with serious repercussions for its largely agrarian human society and local grassland ecosystems.

Warm phases of the AMO are linked to increased rainfall in the Sahel, while the opposite is true during the cold phase. We’ve seen the effects of such a cold phase first hand when the Sahel dramatically dried up from the 1950s well into the 1980s. According to the researchers, another natural cycle called the Pacific Decadal Oscillation (PDO), which is characterized by temperature fluctuations in the northern Pacific Ocean on a scale of 40 to 60 years, also played a major role in the desert’s expansion.

“Deserts generally form in the subtropics because of the Hadley circulation, through which air rises at the equator and descends in the subtropics,” Nigam said. “Climate change is likely to widen the Hadley circulation, causing northward advance of the subtropical deserts. The southward creep of the Sahara, however, suggests that additional mechanisms are at work as well, including climate cycles such as the AMO.”

Lake Chad, which sits in the center of this climatologically conflicted transition zone, serves as a bellwether for changing conditions in the Sahel.

“The Chad Basin falls in the region where the Sahara has crept southward. And the lake is drying out,” Nigam explained. “It’s a very visible footprint of reduced rainfall not just locally, but across the whole region. It’s an integrator of declining water arrivals in the expansive Chad Basin.”

Besides AMO and PDO, human-induced climate change also impacted rainfall variability during the last century. The two natural cycles accounted for about two-thirds of the desert’s total expansion. The remaining third can be attributed to climate change, although the researchers caution that longer climate records which extend over numerous climate cycles would helpful in reaching a more definite conclusion.

This pair of images shows the change in the boundaries of the Sahara Desert during the period 1920-2013, broken down by season. Dotted lines show the boundary as it existed in 1920, while solid lines show the boundary in 2013; both boundaries are averaged across the three months of each season. (Winter = Dec-Feb; Summer = Jun- Aug). Brown shaded regions indicate desert advance while green shaded regions indicate desert retreat. Credit: Natalie Thomas/Sumant Nigam/University of Maryland.

This pair of images shows the change in the boundaries of the Sahara Desert during the period 1920-2013, broken down by season. Dotted lines show the boundary as it existed in 1920, while solid lines show the boundary in 2013; both boundaries are averaged across the three months of each season. (Winter = Dec-Feb; Summer = Jun- Aug). Brown shaded regions indicate desert advance while green shaded regions indicate desert retreat. Credit: Natalie Thomas/Sumant Nigam/University of Maryland.

Obviously, an expanding Sahara — which was already huge, to begin with — means very worrisome news. As Nigam mentioned earlier, other deserts around the world are likely expanding as well. Over 45,000 square miles of arable land are lost to desertification each year, by one estimate — that’s while the world’s population continues to grow, driving food demand up. The United Nations warns that desertification could drive up to 50 million people from their homes, unless humanity cuts back on greenhouse gas emissions.

“The trends in Africa of hot summers getting hotter and rainy seasons drying out are linked with factors that include increasing greenhouse gases and aerosols in the atmosphere,” said Ming Cai, a program director in the National Science Foundation’s Division of Atmospheric and Geospace Sciences, which funded the research. “These trends also have a devastating effect on the lives of African people, who depend on agriculture-based economies.”

In the future, the researchers plan on learning more about what drives desert expansion not only in the Sahara, but in other deserts around the world as well.

“With this study, our priority was to document the long-term trends in rainfall and temperature in the Sahara. Our next step will be to look at what is driving these trends, for the Sahara and elsewhere,” said Natalie Thomas, a graduate student in atmospheric and oceanic science at UMD and lead author of the research paper. “We have already started looking at seasonal temperature trends over North America, for example. Here, winters are getting warmer but summers are about the same. In Africa, it’s the opposite–winters are holding steady but summers are getting warmer. So the stresses in Africa are already more severe.”

Scientific reference: “20th-Century Climate Change over Africa: Seasonal Hydroclimate Trends and Sahara Desert Expansion,” Natalie Thomas and Sumant Nigam, was published online March 29, 2018, in the Journal of Climate.

For the first time in 37 years, it snowed in Sahara

An amateur photographer has captured the dry, barren, Sahara desert in an unlikely situation: covered with a white layer of snow.

The Sahara is the largest hot desert in the world (technically, the Arctic and the Antarctic are also deserts, and they’re both larger).  The average high temperature exceeds 38 to 40 °C or 100.4 to 104.0 °F and sand temperatures are even higher – though nights are much colder. However, it is a myth that the nights are cold after extremely hot days in the Sahara and overall, average temperatures range between 13 °C or 55.4 °F and 20 °C or 68.0 °F. Needless to say, precipitations are extremely scarce and snow is almost a myth. In fact, it’s only the second time in living history it snowed in the Sahara.

Amateur photographer Karim Bouchetata captured the rare phenomenon in photos, saying that the white snow looks spectacular on the bright orange dunes. The snow stayed on for almost a day, which is even more impressive.

“Everyone was stunned to see snow falling in the desert; it is such a rare occurrence,” Mr Bouchetata explained. “It looked amazing as the snow settled on the sand and made a great set of photos. The snow stayed for about a day and has now melted away.”

The last major snowfall – if you can even call it that – hit Ain Sefra in February 1979 when it snowed for a whopping 30 minutes.

Just in case you’re wondering, this isn’t a sign that global warming has slowed its course – in fact, the contrary might very well be true. At this time it’s too early to draw any conclusions.

If you want to see more photos or follow mister Bouchetata, you can do so on his Facebook page.

The eye of the Sahara

A topographic reconstruction (scaled 6:1 on the vertical axis) from satellite photos. False coloring as follows: bedrock=brown, sand=yellow/white, vegetation=green, salty sediments=blue. Credit: NASA

This has got to be one of the strangest places on Earth- – but you couldn’t make much of it if you were just walking by.

It’s located in a rather remote area and the few people who noticed something odd about it didn’t know just how odd it really was. That’s why the 50 km formation didn’t receive much attention until some astronauts made reports about it .

Photo by NASA.

Located in Mauritania, the Eye of the Sahara is not really what you would call a structure, but rather a huge circular formation; it was originally thought to be a crater, but the more recent and accepted theories suggest that it is, in fact, a product of erosion that took place in geological time.

Also known as the Richat Structure, the Eye of the Sahara has been studied by numerous geologists.

“The Richat structure (Sahara, Mauritania) appears as a large dome at least 40 km in diameter within a Late Proterozoic to Ordovician sequence. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks” – small excerpt from a paper.

You can also see it on Google Maps, it’s really a brilliant view, and you can zoom in and out for proportions (coordinates are 21.124217, -11.395569).


Picture sources: 1 2 3

Dust from the Sahara Desert Fertilizes the Amazon’s Forests

The Sahara Desert and the Amazon area have few things in common – one is a dry, barren wasteland, while the other is the most fertile area on Earth. But according to a new NASA study, there may be more than meets the eye when it comes to the two – dust from the Saharan area makes the trans-Atlantic journey, fertilizing the Amazonian rainforest with phosphorus.

The Sahara Desert actually “sends” dust to the Amazon rainforest, via global winds. Image via Wiki Commons.

Sahara is basically an uninterrupted brown band of sand stretching across the entire northern Africa. The Amazon rainforest covers 5,500,000 square kilometres of rainforest in South America, representing over half of the planet’s remaining rainforests, and comprising the largest and most biodiverse environment in the world. But strong winds connect the two areas – the winds sweep across the Sahara, rising dust particles in the air and bringing them all the way to the Amazon, where they help make the area even more fertile with the embedded phosphorous.

A new paper published in Geophysical Research Letters, a journal of the American Geophysical Union, provides the first description of how this happens. Hongbin Yu, associate research scientist at the Earth System Science Interdisciplinary Center (ESSIC) at the University of Maryland and his team estimated how this phosphorous affects the rainforest. In January, he and his team already published a paper which used satellite data to see how much sand reaches the Amazon. Using data collected by a lidar instrument on NASA’s Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite from 2007 through 2013, the team estimates that roughly 22,000 tons of phosphorus make the trans-Atlantic journey each year – that’s very similar to the quantity of phosphorous lost through flooding and water runoff.

This is very important because nutrients, like the ones found in commercial fertilizers, come in short supply in the Amazon – because they are locked in the plants themselves. While decomposing leaves for example do provide nutrients to the soil, phosphorous is generally washed away by rainfall into streams and rivers. In a way, the Amazon basin acts like a “giant leaky bathtub”.

This is where the dust steps in, to compensate that deficit – and it also has an impact on the climate.

“We know that dust is very important in many ways. It is an essential component of the Earth system. Dust will affect climate and, at the same time, climate change will affect dust,” said Yu in a recent statement.

The lidar instrument aboard the CALIPSO satellite sends out pulses of light that bounce off particles in the atmosphere and back to the satellite. It distinguishes dust from other particles based on optical properties.
Image Credit: NASA Goddard’s Scientific Visualization Studio

The data showed that wind and weather pick up on average 182 million tons of dust each year and carry it past the western edge of the Sahara – that’s the equivalent of almost 700,000 trucks filled with sand. 132 million tons remain in the air, while 27.7 million tons (the equivalent of over 100,000 trucks) reach the Amazon. Most of that is phosphorous. What’s interesting is that 43 million tons of dust travel farther to settle out over the Caribbean Sea, in Central America.

Researchers underline the fact that this dust might have a huge impact on the climate and nutrient cycle of many areas, due to the huge quantities involved. However, we can’t establish long term trends based on only this seven year observation, so we need to pay more attention to this cycle, over a longer period of time.

“We need a record of measurements to understand whether or not there is a fairly robust, fairly consistent pattern to this aerosol transport,” he said.

Even within this period, there was significant variation – there was an 86 percent change between the highest amount of dust transported in 2007 and the lowest in 2011, Yu said. It’s not clear why this happens, nor is it clear what impact the dust has on a larger scale, in terms of affecting the climate. But knowing that the Amazonian forest and the Caribbean is affected by something as remote as the Sahara desert is definitely exciting.

“This is a small world,” Yu said, “and we’re all connected together.”


Simulated probability of surface water during the last interglacial. (c) PLOS ONE

Sahara might have been crossed by three large rivers the size of the Nile 100,000 years ago

When the Sahara comes to mind, lush greenery and gorgeous, fast flowing waters might be the last scenery that crosses you. Not too long ago (geological frame), however, the region known today as the Sahara may have been crossed by three giant rivers the size of the Nile, according to a recent palaeohydrological model made by researchers at Hull University, UK led by Professor Tom Coulthard. The paper also discusses the possibility whether one or more of these rivers might have been used as migration routes by early humans leaving central Africa.

Recent evidence reported by other studies suggest that the Sahara was once quite green, dotted with numerous lakes. Considering this, it’s reasonable to assume large flowing waters might have riddled the region in ancient times. Using climate models to estimate rainfall some 100,000 years ago, the Hull researchers constructed a new model which showed ancient monsoons formed 400 miles north of where they do today, spilling rain on mountains in the central Sahara. The huge amounts of water coupled with the terrain’s geometry could have offered the perfect conditions for three large rivers to surface, each approximately the size of the Nile,  also forming vast wetlands in what is now Libya.

 Simulated probability of surface water during the last interglacial. (c) PLOS ONE

Simulated probability of surface water during the last interglacial. (c) PLOS ONE

The westernmost of the three potential ancient Saharan rivers, referred in the paper as the Irharhar, represents the most likely route for human migration from Africa into Europe. The Irharhar river flows directly south to north, uniquely linking the mountain areas experiencing monsoon climates at these times to temperate Mediterranean environments where food and resources would have been abundant – clusters of archaeological sites in Algeria and Tunisia back up the idea, according to the paper published in the journal PLoS ONE.

Unfortunately any “foot prints” these ancient rivers might have left on the Earth are hopelessly buried underneath sand dunes.