As of November 2026, about one-third of Earth's land surface is desert, and a desert is a dry place that gets very little rain. There are four basic types of desert: high pressure, rain shadow, interior continental and coastal. Many deserts lie near 30 degrees latitude, where air that rose and lost its water at the equator comes down dry. Some coastal deserts get almost no rain but are often damp with fog. As of November 2026, in the Atacama Desert, rain of 1 millimeter or more may fall only once every 5 to 20 years.

In a rain shadow, air that rises over mountains cools and drops its moisture; on the lee side the air descends, warms, and the rain is largely shut off. Death Valley is dry because it sits in the rain shadow of mountains, in a long, narrow basin 282 feet, or 86 meters, below sea level, walled in by high, steep mountain ranges. It is also so hot partly because heated air rises, cools, and is recycled back down to the valley floor, where it is compressed and heated even more. As of November 2026, its hottest air temperature ever recorded was 134 degrees Fahrenheit, or 57 degrees Celsius, on July 10, 1913. In the desert heat, drink plenty of water and stay in the shade during the hottest part of the day.

Not every desert is hot, because some deserts have cold winters or are cold all year. The Great Basin is a cold desert that gets less than 10 inches of rain a year, mostly as winter snow. As of November 2026, the largest desert in the world is Antarctica, a cold desert of ice. Polar deserts hold great quantities of water, but most of it is locked in glaciers and ice sheets year-round, so little is available to plants and animals. Sand dunes cover only about 10 percent of the world's deserts; others are dry expanses of rock, salt flats or even ice sheets. The most common dune form on Earth and on Mars is the crescentic dune.

Cacti open their stomata only at night, when the plant is cool, so they lose less moisture through transpiration. A saguaro's skin is covered with a thick waxy coating that waterproofs the plant, and it is pleated like an accordion, so it can expand to hold water after rain. Desert wildflower seeds need a rainstorm of a half inch or more to wash off their protective coating before they can sprout. Seeds of desert annuals can lie dormant for years if conditions are not right for sprouting. After a big rain, flowers can bloom in the desert.

Words to know

• stomata: tiny leaf pores
• transpiration: plant water loss
• latitude: distance from equator
• dormant: resting, waiting
• basin: low land