Deserts Classification based on TemperatureHot Desert Cold deserts Polar deserts
Cold desertsCharacterized by :• cold season in which the rate of temperature declines to 5° C or less during the winter• In summer the temperature becomes high where its average reaches to 30 ° C.• These deserts are situated in continental zones far from the sea.• for example: – Krakom deserts east of the Caspian Sea(the desert of Turkestan) – Great Basin desert in North America.
Hot Desert• These are the deserts which have climates without a severe cold season. the summer is hot and winter is warm, and the temperatures do not drop in winter to 5° C .• Hot deserts can be distinguished into two types:1. Continental desert :far from the coasts of seas, and are characterized by extreme changes in daily temperature – Empty quarter of the Kingdom2. Coastal deserts :which are characterized by limited changes in temperature, where the relative humidity is higher than that of the continental desert, – Peru desert in South America.
Ice Deserts• Covered by ice all the year round and rarely melted, the ice covers all the total area of the desert except 1% of this area, so they are known as White Deserts, Polar Deserts.• These deserts are concentrated on Antarctica, Alaska, the island of Greenland, and in north Eurasia.• The lowest temperature recorded in these deserts was on August 20, 1960 in Vostok where it reached -88.3 ° C• There are water in the form of ice,but, animals can not drink frozen water, and plants can not absorb it by their roots.
1. Extremely Arid Deserts:• These desrets are known as desert areas that can pass a year or more without rainfall, this means that it is not an event repeated annually.• For example, – Empty Quarter of the Arabian Peninsula – the deserts of Atacama in South America.• The area of these deserts is estimated to be 4.4% of the total land area. It also covers a large part of the Arab world.
2. Arid Desert• Those areas with little and irregular rain which does not exceed an annual average of 100 or 125 mm• Mostly the perennial plants in these deserts are restricted only on the low-lying areas.• Generally, the climate of these deserts and the scarcity of rains do not allow cultivating any type of crop.• These deserts occupy about 16.1% of the total area of the land surface and often they cover the edges of the extremely arid deserts.
3. Semi-arid Deserts:• They are those with an average annual rainfall ranges between 125-250 mm, and without perennial plants.• The climate and rains allow cultivating some plants in low- lands that receives more amount of rain runoff.• These deserts occupy around 16.8% of the total land area.
Topography This classification is linked to the former division since the basic factors for distributing dry areas are (wind, temperature, and rain). The Winds directed from land to water (seas and oceans), are dry winds, and the winds directed from water to land are moisture-loaded and their water fall near the coast and may go forward inside until are hampered by high mountains, so deserts are located at: • Areas where the wind directed from land to sea • Areas far from the coast reached by rainy winds. • Areas where the wind has scarce clouds, even if it rains near the beach, no water left can be carried by wind to the interior regions.
The deserts were divided on the basis of geographical locationand the nature of the land (Topography )into four sections: 1. Subtropical Deserts 2. Cool Coastal Deserts 3. Rain-Shadow Deserts 4. Interior-continental Deserts
1. Subtropical Deserts:• These deserts were formed as a result of Semi-permanent Belt from the high pressure formed over the tropical regions, where the air is characterized in Semi-tropical regions with high weight and movement from top to bottom until it reaches the earths surface, and as it descends its temperature and dryness increase.• Some areas are exposed to rains and thunder in summer as a result of wind fronts but these rains still little and not sufficient to reduce drought.• As an example for these deserts is the south-west region of Arabian Peninsula.
2. Cool Coastal Deserts:• In these areas, rainfall is rare although they have cold weather sometimes but they are exposed to the phenomenon of descending air masses with low moisture coming from the cold near seas. The masses of air lose their water over the seas before reaching land because, they exist over the cold water which plays a role in the condensation of water vapor and downloaded it in the form of rain before reaching the neighboring land.• Examples of these deserts, the Namib Desert in Africa, and the Atacama Desert in Peru and Chile in South America, Patagonia desert in the Argentine.
3. Rain-Shadow Deserts:• It means the deserts retained from rain because of the mountains that prevent the arrival of clouds coming from the sea to them, the air loaded with water vapor drops as rains when it hits the feet of the mountains facing the sea, so the masses of the air that reach the far slopes and plains are not able to bring down rains due to the scarcity of water vapor in them.• For example of these deserts, Mohafy desert, and the deserts situated at the west of Asir and Hijaz mountains.
4. Interior-continental Deserts:These deserts are characterized by the lack of the impact of seas on them in addition to being located within the vast tracts of land.• For example: Parts of the Australian desert The polar desert Al-nofood desert.
Activity• What are the characteristics of a desert habitat? [A desert is an area that is very dry and gets less than ten inches of rain per year.]• What kind of adaptations might an animal need to survive in the Sahara desert? [: Answers may vary but could include that an animal would need to be able to stay cool during the day and warm at night.]• If Antarctica is covered with ice and snow, why do you think it is considered a desert? Write a sentence or two to explain your answer. [It is a desert because it probably does not get very much precipitation each year. The snow and ice that are there have accumulated over time.]
Desert – an ecosystem found where there is verylittle rainfall.• Deserts are dry and hot. There are very few clouds.• Two kinds of deserts: – Hot deserts – Cold deserts• Hot deserts – Temperatures are very warm all year round – The summers are very hot• Cold deserts – Short, warm summers – Long, cold winters – Found in places near the north and south poles
Lets see how much you know!• Remember the pictures.• Think about what we talked about.• Think about what you learned.