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A boatman navigates his vessel through dense vegetation in Lake Chad, which has become overgrown. As global warming drives temperatures higher and the Sahara Desert encroaches further, the lake has dramatically reduced in size. The United Nations Environment Programme reports that it is now just a fraction of its 1963 size, down to one-twentieth. Photo credit: Orjan F. Ellingvag/Getty ImagesThe Sahara Desert in northern Africa is steadfastly maintaining its status as the world's largest hot desert. Research from the University of Maryland, published on March 29, 2018, in the Journal of Climate, reveals that the desert has grown by approximately 10 percent over the last century. (The term 'hot desert' distinguishes it from the Arctic and Antarctic, which are classified as cold deserts and are larger in area than the Sahara.)
For a region to be classified as a desert, it must receive no more than 4 inches (100 mm) of rainfall annually. By analyzing rainfall data across Africa from 1920 to 2013, researchers discovered that an additional 10 percent of the surrounding area now meets this criterion, effectively enlarging the world's largest hot desert.
This study marks the first publication to analyze a century's worth of rainfall trends in the Sahara. By examining data and climate models, researchers concluded that roughly two-thirds of the desert's growth resulted from natural variations, while the remaining third was likely driven by human-induced climate change.
The Sahel, a semi-arid grassland, borders the southern edge of the Sahara, acting as a transitional zone between the arid desert and the lush savannas of southern Africa, particularly in Sudan and Chad. Lake Chad, for instance, has been shrinking due to climate variability and agricultural irrigation demands. The persistent lack of rainfall exacerbates the situation.
"The Chad Basin lies within the area where the Sahara has extended southward, and the lake is drying up," explained Sumant Nigam, the study's senior author. "This serves as a clear indicator of reduced rainfall not only locally but across the entire region."
The research also highlights that the Sahara is not the only desert likely expanding. Deserts worldwide are probably undergoing similar climate shifts, leading to their growth. Deserts form through a consistent process: warm air rises in tropical regions near the equator, moves toward the poles, and descends over subtropical areas, where it heats up and dries out. This phenomenon, known as the Hadley cell, is being widened by climate change, increasing the potential area for desert formation and expansion.
The winter of 2018 was unusually severe and prolonged across the northern hemisphere. Even Aïn Séfra, Algeria, located at the Sahara Desert's northern edge, experienced snowfall. In early January, sand dunes were blanketed with up to 16 inches (406 millimeters) of snow, enough for children to sled. Meanwhile, on the opposite side of the globe, Sydney, Australia, recorded a scorching 116 degrees Fahrenheit (46 degrees Celsius) on the same day — the highest temperature in 80 years.
