Where is the tropical desert climate mainly distributed?

The tropical desert climate is distributed in the mainland or the west coast between the Tropic of Cancer and 30 degrees north and south latitude, and extends to inland areas, such as northern Africa, Arabian Peninsula in Asia and desert areas in Australia.

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.

It is controlled by subtropical high pressure area or trade wind area, and it is controlled by tropical continental air mass all the year round, with little rain. The annual precipitation is about 100 mm, and in some places it is only tens of millimeters or even less, 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 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.

Sahara desert in Africa, kalahari desert, Arabian desert in southwest Asia, desert in western and central Australia, desert in Colorado and lower 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.

Main vegetation in tropical desert climate

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.

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 shrub is generally only about 2 meters, the main root can drill into the sand with a depth of 3.5 meters, and the horizontal root can extend to 20~30 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 branchlets. 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. 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 branches of many psammophytes turn 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 the soil with high salt content 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.