What are the reasons for the dryness of deserts in North Africa and Australia?

First, it is controlled by subtropical high.

Subtropical high is a kind of dynamic high, which is a warm high because the air flow over the equator continuously accumulates over the subtropical zone, resulting in downward air flow, which leads to the increase of low-altitude air pressure. The subtropical weather is sunny and dry, mainly because of the prevailing downdraft.

Second, it is controlled by the dry trade wind.

Trade winds are directional winds blowing from subtropical high to equatorial low. Due to the rotation of the earth, the wind direction in the northern hemisphere shifts to the right and becomes the northeast trade wind. It turns left in the southern hemisphere and becomes the southeast trade wind. In the subtropical region of the northern hemisphere, the west coast of the mainland is on the leeward side of the northeast trade wind, and the east coast of the mainland is on the windward side of the northeast trade wind. Similarly, in the subtropical region of the southern hemisphere, the west coast of the mainland is on the leeward side of the southeast trade wind, and the east coast of the mainland is on the windward side of the southeast trade wind. In this way, precipitation in North Africa and Australia is scarce, the climate is dry and there are deserts; But there is more precipitation on the east coast of the mainland, not a desert.

Third, affected by the cold current.

Ocean currents have a great influence on the climate. Cold current can reduce the temperature and humidity of the area it flows through, while warm current can increase the temperature and humidity of the area it flows through. From the world climate and ocean current map, it can be seen that the west coast of subtropical continent is affected by cold current, with scarce precipitation and dry climate; The east coast of the mainland is affected by the warm current, and there is more precipitation.