There is a hidden secret behind the deserts of our planet. From the Sahara to the frozen lands of the Arctic, these arid expanses have one thing in common: a lack of rain. But why do some places on Earth receive much less precipitation than others? Let's dive into the mystery of deserts and discover how they were born and why they remain so dry.
Deserts are the result of global air circulation patterns. Solar energy hits the Earth directly at the equator, heating the air and causing moisture to evaporate. The hot, dry air then moves toward the poles and descends around 30 degrees latitude, according to Lynn Fenstermaker, an ecologist at the Desert Research Institute in Reno, Nevada. This circulation pattern is called the Hadley cell, and it drives the formation of trade winds and many major deserts such as the Sahara, the Gobi, and the Kalahari.
Death Valley (in California, USA) - Wikipedia
However, other factors come into play, such as the interaction between winds and topography. For example, moist air coming from the ocean and meeting a mountain range can lose its moisture as rain or snow as it climbs the slopes. Once on the other side of the mountain, the air becomes dry, creating deserts like the Mojave Desert in California.
Andreas Prein, a scientist at the National Center for Atmospheric Research in Boulder, Colorado, adds that the distance between inland areas and large bodies of water can also influence desert formation. For example, the Gobi Desert in Central Asia is far from the ocean and protected by the Himalayas.
Being coastal does not always mean being humid. Cold ocean currents can create fog that, when moving over land, retains moisture in the air without letting it fall as rain. This can create coastal deserts, like the Atacama in Chile, one of the driest places on Earth. It is also important to note that not all deserts are hot: some regions of the Arctic and Antarctica are considered deserts due to their low precipitation rates.
Climate change also influences the distribution of deserts. For example, thousands of years ago, the Sahara was covered with grasslands and tropical forests. Today, deserts are evolving due to the expansion of Hadley cells, caused by global warming. Higher temperatures can accelerate this process by increasing water evaporation and further drying the air.
Dunes of the Gobi Desert - Wikimedia
Human activities also contribute to landscape transformation. Deforestation to make way for agriculture removes native vegetation, which can reduce precipitation in tropical regions. If more water evaporates instead of being retained in the soil by plants, a vicious cycle gradually dries out landscapes. Semi-arid areas on the edges of existing deserts are particularly vulnerable.
As Andreas Prein points out, "it is often combined factors that favor desert growth. It is not only human activity, or climate change, or natural climate variability, but all of these together that push ecosystems beyond the tipping point."