Deserts are areas where the rainfall is too low to sustain any vegetation at all, or only very scanty scrub. The rainfall in desert areas is less than 25 mm or 10 inches per year, and some years may experience no rainfall at all. The hot deserts are situated in the subtropical high pressure belts where there is unbroken sunshine for the whole year. Such areas include the Sahara, Saudi Arabia, large parts of Iran and Iraq, northwest India, California, South Africa and much of Australia. Here, maximum temperatures of 40 to 45�C are common, although during colder periods of the year, night-time temperatures can drop to freezing or below due to the exceptional radiation loss under the skies.
In summer, temperatures may reach up to 55°C during the daytime , but at night they drop below 0° C.
Most deserts get very little rainfall— on average , not more than 20 cm a year. There may be years without any rainfall at all. Sometimes a lot of rain falls during thunderstorms that last for a few hours.
When the desert dries up after heavy rainfall, salt and other minerals are left behind on the ground. Salt lakes are very common in these places. That is why some desert areas have yellow, brown and red colours.