A habitat with strong contrasts

The desert (from the Latin deserere, to abandon) is a habitat with poor rainfalls. In many deserts, the annual rainfall is below 50 mm, but it can even be zero. In this ecosystem, the shortage of water is the main ecological factor affecting vegetal and animal life.
As well as the shortage of rains, it is also its variability over the year that strongly affects life: for comparison, just think that rainfalls in Europe vary by 20% over the year, while in Sahara this variability reaches 80-150%. This involves occasional violent downpours during which it can rain more than over several consecutive years.
Deserts may be either cold or hot. Cold deserts are at high altitudes, where winter temperatures can be below zero, such as the Gobi Desert, protected by the air masses bringing rain from high mountain ridges.
In hot deserts, the atmospheric temperature during the day can reach 50°C, while the surface temperature of the sand can rise to 90°C. At night, the ground and the air quickly cool down, with temperature differences of over 20°C.
In such a inhospitable environment, all the living beings must adapt themselves: to make up for the shortage of water, the most varied forms of adaptation have developed, even if biodiversity is still low, since between 20 to 400 plant species can be found in 150,000 square kilometres (one half of Italy).

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