Hot deserts cover about one-fifth of the world's land areas. They have mostly clear skies and high temperatures. The average rainfall is under 10 inches a year. Several years may pass with hardly any rain, then a thunderstorm may drench the land. Seeds which have been dormant for years rapidly germinate and many plants flower. When this happens in the Australian desert, people flock to the area to see this superb spectacle.
The world's largest desert is the Sahara in North Africa. It contains sand dunes, plains of loose gravel and bare, rocky uplands. Most plants in hot deserts, such as thorn bushes and cacti, are drought-resistant. The most useful desert animal is the camel. It can go for long periods without water. It loses weight, but regains it when it drinks. Deserts become fertile when they are irrigated (watered). Some deserts, like those of the Middle East, are rich in oil and natural gas. These fuels lie hidden far below the surface.
