On our planet, deserts exist all around the world, including in places very close to the oceans. We know that desert areas are extremely dry, but do you know why?

In our impression, a desert might be an area full of sand, but in reality, there are many different forms of deserts, including endless sand dunes, rocky canyons, thorny grasslands, and polar ice fields, yet they all share a common characteristic: a lack of precipitation.

Boundless Deserts

According to the definition by ecologists who study deserts, generally speaking, places with an annual rainfall of less than 25 centimeters can be considered desert areas.

The scarcity of rainfall means that the air in these regions is very dry, but do you know why some places on Earth receive much less rainfall than others? This is the main cause of deserts.

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In fact, this is primarily caused by the global atmospheric circulation patterns. The equatorial regions of the Earth receive the most direct sunlight, and thus the greatest amount of solar energy, which heats the air and evaporates moisture from it.

This warm, dry air rises and moves towards the Earth's poles, but as it moves to around 30 degrees latitude, it sinks again due to a lack of sufficient driving force.

This pattern of air circulation is known as the Hadley circulation, which drives the formation of the trade winds on Earth. It was these trade winds that propelled early explorers in their navigational adventures.

This is also why many of the world's large deserts, such as the Sahara and Gobi in the Northern Hemisphere, and the Kalahari in the Southern Hemisphere, are located in these mid-latitude regions.

However, the story of desert formation is far more complex than this. Wind patterns interact with topography to jointly influence the location of deserts.Moist air from the ocean direction rises as it hits the mountains, releasing its moisture in the form of rain or snow on the slopes.

When the air crosses the mountains and descends on the other side, it is already very dry, which is how the Mojave Desert in California, USA, is formed, located in the rain shadow area of the Sierra Nevada.

The Mojave Desert, influenced by the Sierra Nevada, is formed.

Inland areas far from the ocean are drier because they are distant from open waters, and by the time the air reaches these areas, it has lost most of its moisture, which is how the Gobi Desert in Central Asia is formed, blocked by the Himalayas.

On the other hand, coastal areas do not always mean moist air, as cold ocean currents colliding with air approaching the coast can produce fog, and when the fog moves over land, the moisture remains in the upper air rather than raining, creating coastal deserts, such as one of the driest places on Earth, the Atacama in Chile.

Of course, not all deserts are hot; the Arctic and Antarctic also have areas that can be considered deserts. Cold air cannot hold moisture like warm air, so despite the large amount of water stored underground in the form of ice in these regions, the cold temperatures at the poles still result in very scarce rainfall.

Oases remaining in the Sahara Desert

As global climate patterns change, desert areas will also change accordingly. For example, you might not believe that thousands of years ago, the area where the Sahara Desert is now was covered with grasslands and tropical forests, and today, climate change is also reshaping the boundaries of deserts around the world.

According to the research of desertologists, due to climate change, the Hadley circulation is expected to continue to expand north and south, which will significantly expand the existing desert areas.

This is because higher temperatures can accelerate the transformation of this desert terrain by increasing water evaporation and further drying the air. In addition to rainfall, the balance of precipitation and evaporation also affects the formation of deserts.On a global scale, as the climate gradually warms, it is expected that there will be increased evaporation from the Earth's surface, which will further expand existing desert areas.

Deforestation

The pressure on natural green spaces by humans is also accelerating this adverse change. The cutting down of trees to plant crops destroys native vegetation, and some studies suggest that deforestation in tropical regions is leading to a decrease in rainfall.

If more water on the surface is evaporated rather than being retained in the soil by vegetation, the air in these areas will become increasingly dry. Currently, the ecological environment of semi-arid regions near the edges of deserts is particularly fragile, and without protection, it may degrade into desert areas.

These complex factors are accelerating the expansion of desert areas, not just human activities, but also climate change and changes in the natural environment. These adverse changes are pushing ecosystems beyond critical thresholds.