Humanities › Geography Desert Definition and Characteristics Arid Lands and Deserts Lose More Water Than They Gain Share Flipboard Email Print 35007 / Getty Images Geography Physical Geography Basics Political Geography Population Country Information Key Figures & Milestones Maps Urban Geography By Matt Rosenberg Geography Expert M.A., Geography, California State University - Northridge B.A., Geography, University of California - Davis Matt Rosenberg is an award-winning geographer and the author of "The Handy Geography Answer Book" and "The Geography Bee Complete Preparation Handbook." our editorial process Matt Rosenberg Updated January 21, 2019 Deserts, also known as arid lands, are regions that receive less than 10 inches of precipitation a year and have little vegetation. Deserts occupy about one-fifth of the land on Earth and appear on every continent. Little Precipitation The little precipitation and rain that falls in deserts is usually erratic and varies from year to year. While a desert might have an annual average of five inches of precipitation, that precipitation may come in the form of three inches one year, none the next, 15 inches the third, and two inches the fourth. Thus, in arid environments, the annual average tells little about actual rainfall. What does matter is that deserts receive less precipitation than their potential evapotranspiration (evaporation from the soil and plants plus transpiration from plants equals evapotranspiration, abbreviated as ET). This means that deserts do not receive enough precipitation to overcome the amount evaporated, so no pools of water can form. benedek / Getty Images Plant and Animal Life With little rainfall, few plants grow in desert locations. When plants do grow, they are usually spaced far apart and are quite sparse. Without vegetation, deserts are highly prone to erosion since there are no plants to hold down the soil. Despite the lack of water, a number of animals call deserts home. These animals have adapted to not only survive, but to flourish, in harsh desert environments. Lizards, tortoises, rattlesnakes, roadrunners, vultures, and, of course, camels all live in deserts. Flooding in a Desert It doesn't rain often in a desert, but when it does, the rain is often intense. Since the ground is often impermeable (meaning that water isn't absorbed into the ground easily), the water runs quickly right into streams that only exist during rainfalls. The swift water of these ephemeral streams are responsible for most of the erosion that takes place in the desert. Desert rain often never makes it to the ocean, the streams usually end in lakes that dry up or the streams themselves just dry up. For instance, almost all of the rain that falls in Nevada never makes it to a perennial river or to the ocean. Permanent streams in the desert are usually the result of "exotic" water, meaning that the water in the streams comes from outside of the desert. For example, the Nile River flows through a desert but the river's source in high in the mountains of Central Africa. Where Is the World's Largest Desert? The world's largest desert is actually the very cold continent of Antarctica. It is the world's driest place, receiving less than two inches of precipitation annually. Antarctica is 5.5 million square miles (14,245,000 square kilometers) in area. Outside of polar regions, Northern Africa's Sahara Desert is the world's largest desert at more than 3.5 million square miles (nine million square kilometers), which is slightly smaller than the size of the United States, the world's fourth largest country. The Sahara stretches from Mauritania to Egypt and Sudan. What Is the World's Hottest Temperature? The world's highest temperature was recorded in the Sahara Desert (136 degrees F or 58 degrees C at Azizia, Libya on September 13, 1922). Why Is a Desert so Cold at Night? The very dry air of the desert holds little moisture and thus holds little heat; thus, as soon as the sun sets, the desert cools considerably. Clear, cloudless skies also help to quickly release heat at night. Most deserts have very low temperatures at night. Desertification In the 1970s, the Sahel strip that stretches along the southern fringe of the Sahara Desert in Africa experienced a devastating drought, causing land that was formerly used for grazing to turn to desert in a process known as desertification. Approximately one-quarter of the land on Earth is threatened by desertification. The United Nations held a conference to begin discussing desertification in 1977. These discussions eventually resulted in the establishment of the United Nations Convention to Combat Desertification, an international treaty established in 1996 to combat desertification.