Characteristics of tropical desert climate

Tropical desert climate has many characteristics, such as sunny days, strong sunshine, dryness, hot summer, large temperature difference between day and night, and many sandstorms. The key is "doing". Because it is dry, there is less rain, more sunshine and strong sunshine; Because it is dry, there is no cloud in the sky, so it can't stop some sunshine, and there is no water on the ground, so it can't evaporate and cool down. All the heat from the sun on the ground is used to heat the earth and the air, so the temperature in summer is particularly high, and the temperature difference between day and night is particularly large. Because of the dry weather, there are few plants on the ground. When there is wind, it will blow sand. The high temperature on the desert surface makes the temperature difference between the upper and lower atmosphere close to the ground extremely large. However, the temperature distribution of cold air layer and hot air layer can reflect the distant scenery in front of travelers, which is called a mirage in meteorology, commonly known as a mirage. Therefore, travelers in the desert often see a blue lake in front of them. In fact, it is the reflection of the distant sky that makes them happy. On the black asphalt pavement in summer afternoon, you can often see a piece of blue water on the road ahead. When you take a closer look, it disappears and moves to the front. This is also a mirage scam on the road. The four seasons in the desert are also very different from other places at the same latitude. In eastern China, the spring and autumn seasons are very short because of the monsoon continental climate. However, in desert areas, spring and autumn are shorter. Because the desert area is too dry, there is no water regulation. The temperature rises in a straight line in spring and falls in autumn. The sum of spring and autumn is only about two and a half months to three months. Spring and autumn are short, and winter and summer are particularly long, so some people describe it as: "In the arid areas of Central Asia, there are only two seasons in a year: winter in Siberia and summer in the Sahara." There is some truth in this statement. The temperature change of desert climate is the most extreme among all kinds of climate in the world. Specifically, the tropical desert climate zone has the following climatic characteristics:

The climatic characteristics of tropical desert can be summarized as follows: dry and hot all year round, especially in hot season. The tropical desert climate is mainly distributed in the mainland or the west coast of the mainland near the Tropic of Cancer, mainly in the narrow areas of North Africa, West Asia, central and western Australia and western South America, generally in the mainland and west coast near the Tropic of Cancer. Take North Africa, Arabian Peninsula in Asia and desert areas in Australia as typical examples. It is characterized by high annual average temperature, large annual temperature difference, large daily temperature difference and scarce precipitation. The annual precipitation is generally below 250 mm, and in many areas it is only tens or even several millimeters. Precipitation varies greatly, and it often doesn't rain for several years.

Tropical desert (dry) climate is generally distributed in the mainland and west coast controlled by the north-south regression high pressure belt, with desert areas in North Africa, Arabian Peninsula in Asia and Australia as typical examples. Controlled by subtropical high pressure zone or trade wind zone, it is controlled by tropical continental air mass all the year round, with drought and little rain. The annual precipitation is about 100mm, and in some places it is only a few tens of mm, with plenty of sunshine and high temperature. The average temperature in the hottest month can reach about 30℃. The contradiction between heat and water is prominent. The distribution and formation of the world's great deserts are closely related to the tropical dry climate. The natural vegetation is desert.

Sahara Desert in Africa, kalahari desert, Arabian Desert in Southwest Asia, thar desert, deserts in western and central Australia, deserts in Baja Colorado and California in North America and Atacama Desert in South America all have typical tropical desert climate. The tropical desert climate zone is on the north and south sides of the tropical grassland climate zone. The air pressure in these places is high and the weather is stable. The wind always blows from the land to the sea, but the humid air from the sea can't enter the land, so the rainfall is very small and very dry. The rocks on the ground are weathered to form tiny sand grains, which float and accumulate with the wind, forming sand dunes, which are widely distributed and become vast deserts. In some places, the weathering speed of rocks is slow, forming large gravel, which is desert. The area of desert on the earth is very vast, and there is a trend of further expansion.

The tropical desert climate appears in the subtropical high and trade winds on the west coast and inland of the mainland. The Sahara Desert in Africa, kalahari desert, Arabian Desert in Southwest Asia, thar desert, deserts in western and central Australia, deserts in the lower reaches of Colorado and California in North America, and Atacama Desert in South America all have typical tropical arid climates. Controlled by the downward airflow of subtropical high all the year round, there is little precipitation, with the annual precipitation below 250 mm. In some places, it doesn't rain for several years, and the evapotranspiration may be more than 20 times larger than the precipitation. The annual average temperature is higher than 18℃, and it is very hot in summer. The average temperature in the hottest month is mostly 30℃-35℃, the absolute maximum temperature in some places is as high as 58℃, the maximum temperature on the ground is above 80℃, and the average temperature in Leng Yue is not lower than 10℃. The daily temperature difference can reach 35℃-40℃, and the minimum temperature at night can be reduced to about 0℃. Less clouds, strong sunshine and abundant solar energy resources. The tropical desert region has dry climate, high temperature, heavy sandstorm and high soil salt content. In order to survive and grow, plants must have a strange ability to adapt to the natural environment in the desert. Therefore, compared with plants in general areas, plants in desert are quite different in appearance, internal structure and physiological functions.

The main features are:

(1) Most perennial psammophytes have strong roots to increase water absorption in sandy soil. Generally, the root depth and width are many times wider than the plant height and plant width. Horizontal roots (lateral roots) can spread far away in all directions without layering, but spread evenly to avoid being concentrated in one place and consuming too much water in the sand layer. For example, the plant height of Salix psammophila is generally only about 2 meters, the main roots can drill into the sand with a depth of 3.5 meters, and the horizontal roots can extend to 20 to 30 meters. Even if wind erosion exposes a layer of horizontal roots, it will not cause the whole plant to die. The lateral roots of willow planted for only one year can reach 1 1 m. But some annual plants have shallow roots, and it rains occasionally in spring, even if it is rare. As long as the surface is wet, they will make full use of it, grow vigorously, blossom and bear fruit, and complete their life cycle in a short time, thus avoiding dry and hot summer. People call them "ephemeral plants".

(2) In order to reduce water consumption and transpiration area, the leaves of many plants shrink very little, or become rod-shaped or spiny, or even leafless, and photosynthesis is carried out with twigs. Haloxylon ammodendron is leafless and assimilated by green branches, so it is called "leafless tree". Some plants not only have small leaves, but also small flowers, such as tamarisk (red willow). In some plants, in order to inhibit transpiration, the epidermal cell wall strength of leaves is lignified and the cuticle is thickened, or there is a waxy layer and a lot of hair on the surface of leaves, and the stomata of leaf tissues are intercepted and partially blocked.

(3) The surface of branches of many psammophytes turns white or grayish white to resist the strong sunshine in summer and avoid being scorched by the high temperature of the sand surface, such as Calligonum mongolicum.

(4) Many plants have strong germination ability and strong lateral branch toughness, which can resist the attack of sandstorm and sand burial. Tamarix (red willow) is like this. Sand burial can still produce adventitious roots and sprout more vigorously. In desert and Gobi areas, the wind and sand activities are strong, and Tamarix chinensis growing in low-lying wetlands is often attacked by quicksand, which makes shrubs accumulate sand continuously. However, Tamarix chinensis can continue to grow due to the action of adventitious roots after being buried in sand, so a rising tide lifts all boats, forming a tall shrub sand pile (sandbag).

(5) Many plants are succulents with high salt concentration, which can absorb water from high salinity soil to maintain their lives, such as Suaeda salsa and salt claws.

Plants in the desert spread their seeds in a strange way. Many annual or perennial plants have wings or hairs on their seeds. When the seeds are ripe, they will fly with the wind and sprout and grow when they meet the right place. For example, the seeds of Tamarix chinensis are very small and have white crown hairs (bunches of hairs). If they are blown off by the wind and planted naturally, the germination rate of seeds can reach more than 80%. Once the seeds fall on the low-lying wetland, they can germinate and emerge in 2 ~ 3 days and grow rapidly. Other plants, such as flowering branches, have nodes and pods, which fall intermittently in mature season, and each node swells into a ball and is lighter in weight. When it meets the wind, it rolls on the sand surface without being buried in the sand, and germinates and grows quickly when the conditions are right. The seeds of another kind of Artemisia ordosica, after encountering a little rain, immediately ooze gum, commonly known as "Artemisia ordosica gum", become sticky, roll on the sand dunes with the wind, and germinate when a large amount of sand adheres to the whole body. Sub-Saharan Africa is the most typical region of tropical desert climate. The Sahara Desert is the largest desert in the world except Antarctica. It is located in the north of Africa, with extremely harsh climatic conditions, and it is one of the most unsuitable places for biological growth on earth. Sahara means "big desert" in Arabic. Located in the southern Atlas Mountains and the Mediterranean Sea (about 35 N), about14 N (250 mm isohyet), it starts from the Atlantic coast in the west and reaches the Red Sea coast in the east. It spans the northern part of the African continent, with a length of 5,600 kilometers from east to west and a width of 1600 kilometers from north to south, with a total area of about 906.5㎞? It accounts for about 32% of Africa's total area. You can put the whole of America in. The name "Sahara" comes from Arabic, which is introduced from the language of Tuareg, a local nomadic people, and means "desert" in their language. This desert was formed about 2.5 million years ago.

The Sahara desert starts from the Atlantic coast in the west, reaches the Atlas Mountains and the Mediterranean Sea in the north, the Red Sea in the east and the Sudan and Niger River basins in the south. The Sahara desert is divided into several parts: Western Sahara; Central plateau mountainous areas (including Ahagar Plateau in Algeria, Aier Plateau in Niger and Tibesti Plateau in Chad; The eastern part is the most desolate area, especially the Tenare Desert and the Libyan Desert. The highest point of the Sahara Desert is Kuxi Mountain in Tibesti Plateau, with an altitude of 34 15m.

The Sahara desert divides the African continent into two parts, North Africa and Southern Black Africa. The climate and culture of these two parts are completely different. The southern border of the Sahara desert is semi-arid savanna, which is called "Sahel" in Arabic, and then it is called "Sudan" in Arabic, which means black Africa. Asia: Riyadh (Saudi Arabia), Mecca (Saudi Arabia), Jeddah (Saudi Arabia), Manama (Bahrain), Doha (Qatar), Abu Dhabi (UAE), Dubai (UAE), Muscat (Oman), Sana 'a (Yemen), Aden (Yemen), Kuwait (Kuwait) and Basra (Iraq).

The highest temperature in Basra reaches 58℃, which is called "the world's hot pole".

Africa: Aswan (Egypt), Bechard (Algeria), Nouakchott (Mauritania), Port Sudan (Sudan), Djibouti (Djibouti), Windhoek (Namibia).

Oceania: Alice Springs (Australia), port hedland (Australia)

North America: Phoenix (USA), sicali (Mexico) and Hermosillo (Mexico).

South America: Lima (Peru), Aarika (Chile), Iquique (Chile)

Iquique has a record of no precipitation for 14 years, which is called "the drought pole of the world".