Since 1920, the Sahara has grown steadily. Its size would have increased by about 10%, according to a scientific study that was recently published. The world’s largest dry desert is expected to grow again and that’s not good news. Explanations.
Deserts are usually defined by their low annual rainfall, usually 100 millimeters of rain per year or less. Researchers analyzed rainfall data from across Africa from 1920 to 2013 and found that the Sahara, which occupies much of the northern part of the continent, grew by 10% during this period, looking at annual trends. According to this data, other deserts could also be increasing in size.
“Our results are specific to the Sahara, but there are probably parallels to be made with other deserts in the world,” says Sumant Nigam, professor of atmospheric and oceanic sciences at the University of Maryland, lead author of the study, quoted in the American scientific journal The Journal of Climate.
The results of the study suggest that man-made climate change as well as natural climate cycles such as the Atlantic multidecadal oscillation (AMO), a change in sea surface temperature that spans several decades, from 40 to 80 years, observed in the North Atlantic Ocean by subtracting the linear variation due to global warming, EdL) caused the expansion of the desert. The researchers concluded that these natural climatic cycles accounted for about two-thirds of the total observed expansion of the Sahara. The remaining third can be attributed to the impact of man-made pollution.
After the deserts of the Arctic and Antarctic, the Sahara is the largest dry desert in the world. It is about the same size as the United States. Its boundaries fluctuate seasonally, extending into a dry winter and contracting during the wetter summer.
According to the US scientists, the Sahara is spreading as the Sahel, which adjoins it, recedes. This disrupts the fragile grassland ecosystems and human societies of the region. Lake Chad, located in the center of this climatologically conflicting transition zone, serves as a reference for changing conditions in the Sahel. “The Chad Basin is in the region where the Sahara is expanding and the lake is drying up,” says Sumant Nigam. “It is a very visible footprint of rainfall reduction not only locally, but throughout the region. ”
The results of the study suggest profound changes in the future for the Sahara as well as for other subtropical deserts around the world. As the world’s population continues to grow, a reduction in arable land with enough rainfall to support crops could have “devastating consequences,” according to the scientists.
“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, director of the Division of Atmospheric and Geospace Sciences at the National Science Foundation, which funded the research. “These trends also have a devastating effect on the lives of African people, who depend on agriculture-based economies.”
This research is the first to evaluate the changes in the largest desert in the world in almost one hundred years. The most notable expansion of the Sahara occurred in summer, growing almost 16%.