20% of the land in the world is desert. How did so many deserts come into being?

When it comes to deserts, we always mention about the overuse of land and deforestation by human beings. So, is the desert caused by human beings? In fact, human activities such as unreasonable use of land, indiscriminate cultivation and deforestation, overloading and overgrazing have indeed destroyed the surface vegetation, resulting in the bare ground, and the sand has been blown up by the strong wind, forming sand dunes. However, these plots are different from deserts and are generally called sand areas.

Human beings can promote or delay the formation and expansion of deserts, but the main reason for the formation of deserts also lies in nature. Dry, little rain and strong wind are the necessary conditions for the formation of deserts. Dry and rainless, which makes most plants unable to survive. The ground lacks vegetation coverage, the soil moisture content is low, and the soil is loose. The strong wind (the wind that forms the desert, mainly the wind of level 3-7) causes the sand and soil to be eroded and transported by the wind. When the wind weakens or meets obstacles, the sand and soil will be deposited to form sand dunes. With the wind blowing, the sand will be piled into sand dunes. When many sand dunes are connected into a piece, it will become a vast desert.

However, just a dry, rainless, and windy climate does not necessarily lead to deserts. Abundant sources of sand are another condition for the formation of deserts. For example, the climate in the eastern Xinjiang of China, the Western Alxa Plateau, and its marginal Highlands, the Tarim Basin, Qaidam Basin and the foothills of the Hexi Corridor is dry and windy, but it is not a desert area, but a Gobi with flattened bare bedrock or rock debris and gravel. It can be seen that abundant sediment sources are the material basis for the formation of deserts. There are three main sources of sand: river alluvium, river lake sediment, and rock weathering.

To sum up, deserts are formed by two essential factors: climatic conditions and abundant sources of desert sand, both of which are indispensable. Human behavior can affect the speed and scale of desert formation, but it is not an essential factor for desert formation.