The Sahara Desert Is Getting Bigger

The Sahara desert is getting bigger, creating further problems for those already suffering from poverty and drought, especially in the neighboring Sahel. This was the result of a study published by researchers from the American University of Maryland in the journal “Journal of Climate”.

The authors analyzed precipitation data from across Africa for the period 1920-2013. Deserts are usually defined by the amount of rain that falls in a region. If it is less than 100 millimeters per year, it is considered a desert.

“Affected countries do not notice”

As it turned out, the area with such low rainfall on the northern and southern edges of the Sahara during the observation period expanded by ten percent. “Many previous studies have documented precipitation trends in the Sahara and the Sahel,” says main study author Natalie Thomas. “But our work is unique because it captures the changes in a desert area on the scale of a century.”

Of particular concern to researchers is the seasonal trend. Every summer, the largest desert in the world grows even stronger, by 16 percent. It usually falls during this season, most of the rain, so that the arid area actually shrink and should only grow in winter. But the precipitation has been decreasing for some time. “The result is very impressive because the summer season is the most important growth period for agriculture,” explains study author Sumant Nigam. “But the governments of the affected countries Chad and Sudan take no notice of it.”

Desertification changes are related to natural factors and man-made climate change. For example, longer- term climate oscillations such as the Pacific and Atlantic Multidecadal Oscillation (PMO and AMO), which alternate at intervals of several decades between cold and warm phases, influence weather patterns in northern Africa.

For the AMO, the cycle is 50 to 70 years. In the warmer phase, there is more rain in the Sahel and less rain

in the cooler period. Thus, the catastrophic drought that prevailed in the region in the 1950s to the 1980s can be assigned to such a cold phase. The 40 to 60-year PDO cycle also plays a role.

The effect could also work on other deserts

Using statistical methods, the study authors were able to determine the influence of these factors on precipitation variability. Accordingly, the observed extent of the Sahara is attributable to two-thirds of the natural fluctuations, one third to the anthropogenic global warming. “Our results are specific to the Sahara,” says Nigam. “But they probably have implications for the other great deserts of the earth.”

The expansion of the desert to the south in conjunction with the reduced rainfall has noticeable consequences for the neighboring areas, the Sahel and Chad. There the vegetation withers and the soils dry out, which has a devastating effect on agriculture there.

Dramatic changes in Lake Chad

Similarly dramatic are the changes in the vast Chad Basin in western Central Africa, where Lake Chad lies. With its tributaries, it is an important source of water for more than 30 million people. But over the past 50 years, he has lost most of his water.

The northern lake basin even dried up completely in the 1970s. “The level has dropped rapidly,” affirms

Nigam. “But we can not attribute the decline solely to precipitation, because the residents also take water

from the lake. But he’s in the zone approaching the Sahara. “

However, the amount of water in the lake increased again around 1998, and in recent years the level has stabilized again. Some researchers suspect that it could even grow again in the future, with inflows from groundwater reservoirs filling it up.

Devastating consequences for people in Africa

The expansion of the Sahara, fear Thomas and her colleagues, could accelerate in the future. Deserts arise in subtropical areas due to a certain atmospheric circulation, the so-called Hadley cells. Warm air rises in the tropics near the equator, creating dense clouds of rain and thunderstorms. At high altitude, it encounters a boundary layer of the atmosphere (tropopause) and is deflected to the north and south.

Over the subtropics, the warm air masses sink again, but are now dry, because the moisture remained in the tropics. This is where deserts and other arid areas are formed. “Climate change is likely to extend the Hadley circulation so that these zones move north,” says Nigam. “The fact that the Sahara is crawling southwards could mean that there are other mechanisms at work, such as the AMO.”

This is not good news for the world. The global population continues to grow as any loss of buildable land could have catastrophic consequences. “In Africa, the summers are getting hotter and the rainy seasons less precipitous, which is related to factors such as increasing levels of greenhouse gases and aerosols in the atmosphere,” notes atmospheric researcher Ming Ca of the US National Science Foundation. “These trends are having a devastating impact on the lives of those on the continent whose economies are mainly based on agriculture.” Africa is the least responsible for climate change, but most vulnerable to it.