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In geography, desert is defined as an area of the earth’s surface in which the precipitations are unlikely to exceed 250 millimeters per year, and the soil is mostly arid, with little or no vegetation.
Among the deserts, according to this definition, must also be considered Polar Regions, in addition to the more familiar arid areas that are located at medium and low latitudes.
You can distinguish three main types:
- Hot deserts, rocky deserts where the soil is made up of stones or pebbles called by the Arabic word Hamada; it can also be gravelly, called Reg, or sandy dunes, called Erg, present in tropical regions, characterized by enhanced aridity, vegetation reduced or absent, lack of perennial streams, tendency to drought; climate which is associated with that environment is the hot desert climate (according to the Köppen climate);
- Cold deserts (also called, somewhat inaccurately, “temperate deserts”), present in continental temperate regions, characterized by strong aridity and remarkable annual thermal excursions, with hot summers and cold winters; climate which is associated with that environment is the cold desert climate (according to the Köppen climate);
- Polar deserts (White Deserts), present in the northern and the southern margin of the boreal and southern continents (Greenland, the Arctic and Antarctica), characterized by intense cold and perennial expanses of snow and ice; climate which is associated with that environment is the glacial climate (according to the Köppen climate).
Hot Desert Erg, Tunisia.