Areas of the barren land of the Sahara Desert, the largest hot desert in the world, have surprisingly turned green, NASA satellite images show.
The desert is one of the driest places on Earth, but it was once covered in vegetation and lakes somewhere between 11 and five thousand years ago.
Known as the African Humid Period, the earth’s tilt changed, bringing the Northern Hemisphere closer to the sun during the summer. This caused a low pressure system that brought moisture from the Atlantic into the desert.
This was not a one time event – scientists have identified over 230 periods of greening over the past eight million years, occurring roughly every 21,000 years.
The region recently experienced unprecedented heavy rainfall which left over half a foot (over 15 centimetres) of rain in some areas.
New satellite imagery reveals patches of plant life emerging in desert regions in Morocco, Algeria, Tunisia and Libya. Shrubs and trees have begun to grow in low-lying areas such as riverbeds.
The greenery is the result of an extratropical cyclone on September 7 and 8 that brought torrential rains to that part of northwestern Africa, which rarely sees any. Indeed, on average the Sahara receives under eight centimetres of rain per year, with over half receiving less than three. Rainfall events are rare, occurring less than once a decade on average, according to Weather & Radar.
However, while rain fell mostly on sparsely populated areas, floods killed more than a thousand people and affected four million across 14 African countries, damaging roads and disrupting electricity and water supplies according to the World Food Programme and the Associated Press.
According to scientists, plant life responds quickly to heavy rain events in northwestern Africa for a brief period, turning dunes into green landscapes.
“While [there is] some degree of rainfall in this region… every summer, what’s unique this year is the involvement of an extratropical cyclone,” said Moshe Armon, a senior lecturer at the Institute of Earth Sciences and the Hebrew University of Jerusalem.
The abnormal rainfall was triggered by the northward movement of the tropical rain belt, known as the Intertropical Convergence Zone (ITCZ), which reached far further north than usual. The Southern Hemisphere winds blowing from the southeast converged with the Northern Hemisphere winds blowing from the northeast. The combination of converging winds, strong sun and warm ocean water results in moist air and continuous clouds, rain and thunderstorms.
Typically, there are heavy rains in equatorial regions such as the Democratic Republic of Congo and Uganda, but this time they drenched the Sahara.
According to the Washington Post, scientists are not sure why the ITCZ moved so far north this year. It could be due to near-record warmth in the North Atlantic Ocean, increasing the temperature difference between the Northern and Southern hemispheres, said Francesco S.R. Pausata, an atmospheric science professor at the University of Quebec in Montreal who has studied the ITCZ.
There could also be a connection to global warming heating the Northern Hemisphere more than the Southern: “The Northern Hemisphere, as there is more land than the Southern Hemisphere, tends to warm up more and hence it could push the ITCZ further north,” Pausata said.
The most significant increase in greenness over the last year is shown across the strip of north-central Africa, covering southern Mauritania, southern Mali, Burkina Faso, southern Niger, northern Nigeria, southern Chad, southern Sudan, and portions of South Sudan, Eritrea, Ethiopia, and Kenya.
At the same time, southern regions which have received significantly less rain than usual, including Guinea, Ghana, central to southern Nigeria, Cameroon and a portion of western Ethiopia, have seen the greatest decrease in greenness compared to last year.
