Why does Riyadh have a tropical desert climate but precipitation is concentrated in winter?

The atmospheric environment ranks first and is controlled by the subtropical high pressure belt. The subtropical high is a dynamic high pressure. It is formed because the air above the equator continuously flows to and accumulates above the subtropical zone, causing downdrafts and causing the low air pressure to increase. It is a warm high pressure. The main reason for sunny and dry weather in the subtropical region is the prevalence of downdrafts. Second, it is controlled by dry trade winds. Trade winds are directional winds that blow from the subtropical high pressure zone to the equatorial low pressure zone. Due to the rotation of the earth, the wind direction is deflected, deflecting to the right in the northern hemisphere and becoming the northeast trade wind; in the southern hemisphere, it deflects to the left and becoming the southeast trade wind. In the subtropical region of the Northern Hemisphere, the west coast of the continent is on the leeward side of the northeast trade wind, and the east coast of the continent is on the windward side of the northeast trade wind; similarly, in the subtropical region of the southern hemisphere, the west coast of the continent is on the leeward side of the southeast trade wind, and the east coast of the continent is on the windward side of the southeast trade wind. In this way, the west coast of the continent in the subtropical regions of the southern and northern hemispheres has less precipitation, a dry climate, and desert distribution; while the east coast of the continent has more precipitation and is not a desert. Third, affected by the cold wave. Ocean currents have a great influence on climate. Cold currents have the effect of cooling and dehumidifying the areas they pass through, while warm currents have the effect of warming and humidifying the areas they pass through. It can be seen from the "World Climate and Ocean Currents Map" that the west coast of the continent in the subtropical region is affected by cold currents, so precipitation is scarce and the climate is arid; the east coast of the continent is affected by warm currents, so precipitation is more. As for the causes of the tropical desert climate in the subtropical continental interior, in addition to being affected by the subtropical high pressure or dry trade winds, it is also related to the fact that it is far away from the ocean and is less affected by the ocean. Temperature and Humidity Tropical Desert Climate Tropical desert climate occurs on the west coast of the continent and in the interior of the continent in the subtropical high pressure belt and trade wind belt. This area is controlled by subtropical high pressure downdrafts all year round. From the perspective of the entire earth, the formation of dry climate areas (arid areas) is mainly related to factors such as latitude and atmospheric circulation. Between 15 and 35 degrees north and south latitude, it is the area controlled by the subtropical high pressure belt (also known as the returning high pressure belt) and is blown by the trade winds all year round. The air in the high-pressure zone has a sinking effect. When the air sinks, it forms adiabatic warming, which reduces the relative humidity and makes the air very dry. The trade wind is a stable wind blowing from the subtropical high-pressure belt to the equatorial low-pressure belt. It continues to heat up as it blows toward the equator. The hotter the air, the greater the amount of water it consumes, resulting in a very dry dry wind. In this way, in the area controlled by the subtropical high pressure belt, the atmosphere is very stable, the humidity is low, there are few clouds and little rain, making it an arid area on the earth with scarce rainfall. Most of the world's largest deserts are located here, such as the Sahara Desert in North Africa, the Arabian Desert in Southwest Asia, and the Atacama Desert in South America. Therefore, it is known as the "return to the desert belt". The formation of tropical desert climates varies slightly from place to place. The tropical desert climate distribution area on the west side of South America is narrow and long. Reasons: ① The Andes is located on the west coast of the South American continent, which makes the tropical desert climate distribution area narrow. ②The Peruvian cold current passes through the west side, cooling and dehumidifying. ③It is located on the leeward slope of the southeast trade wind and receives less precipitation. The causes of Pakistan's tropical desert climate are almost unique in the world. The causes are mainly affected by the following two aspects: One reason: the serious destruction of ancient forests and other vegetation. Reason two: Blocked by the mountains on the edge of the Iranian Plateau, the southwest monsoon is difficult to reach or penetrate deeply.

Reference: Baidu Encyclopedia Hope it helps you