EarthSky | The Sahara Desert is growing
The Sahara is already the world’s largest warm-weather desert – about the size of the contiguous United States. And according to a new study, the desert has expanded over the past century.
Deserts are generally defined by their low average annual rainfall – typically less than 4 inches (100 mm) of rain per year or less. For the new study published on March 29, 2018, in the peer-reviewed journal Climate Journal, the researchers analyzed rainfall data recorded across Africa from 1920 to 2013 and found that the Sahara, which occupies much of the northern part of the continent, expanded by 10 percent during this period. .
Researchers suggest other deserts could expand as well. Sumant Nigam is professor of atmospheric and ocean sciences at the University of Maryland and lead author of the study. He said in a statement:
Our results are specific to the Sahara, but they probably have implications for other deserts around the world.
The study’s results suggest that human-caused climate change, along with natural climate cycles such as the Atlantic Multidecadal Oscillation (AMO), caused the expansion of the desert. Nigam said:
Deserts usually form in the subtropics due to the Hadley circulation, through which air rises at the equator and descends in the subtropics. Climate change is likely to widen Hadley’s circulation, causing the subtropical deserts to advance north. The southward creep of the Sahara suggests, however, that additional mechanisms are also at work, notably climate cycles such as AMO.
Find out how scientists identified the effects of man-made climate change here.
The southern border of the Sahara adjoins the Sahel, the semi-arid transition zone that lies between the Sahara and the fertile savannas further south. The Sahara expands as the Sahel recedes, disrupting fragile grassland ecosystems and human societies in the region. Nigam said Lake Chad, which lies at the center of this climate conflict transition zone, serves as a barometer for changing conditions in the Sahel. He explained:
The Chad Basin is located in the region where the Sahara has slipped south. And the lake dries up. This is a very visible imprint of reduced precipitation, not only locally, but across the region. It is an integrator of the drop in water inflows in the vast Chad basin.
Conclusion: A new study indicates that the Sahara Desert has grown by 10% over the past century.
Read more from the University of Maryland