The term “high desert” describes a geographical landscape where aridity is compounded by significant elevation. While all deserts lack moisture, altitude introduces unique environmental pressures that fundamentally change the climate and resulting ecosystems. This classification is primarily descriptive and regional, differentiating these elevated, often colder, arid zones from lower-elevation, consistently hot deserts. High deserts are defined by a combination of the rain shadow effect, which causes dryness, and high ground, which introduces temperature extremes.
The Elevation Criteria
The classification of “high desert” is not governed by a single, internationally agreed-upon scientific standard. Instead, it serves as a regional distinction to contrast with nearby “low deserts.” In the United States, particularly the Southwest, the high desert is commonly considered to begin around 2,000 feet (610 meters) above sea level. Many regions classified as high desert, such as portions of the Great Basin, reach elevations of 4,000 to 6,000 feet (1,200 to 1,800 meters) or more.
This elevation is relevant due to fundamental atmospheric processes, specifically the rain shadow effect and adiabatic cooling. Mountain ranges force moist air upward, causing it to cool and release precipitation on the windward side, leaving the high desert dry on the leeward side. The decrease in air pressure and temperature that occurs with rising altitude, known as the lapse rate, is responsible for the overall cooler climate compared to low deserts.
Defining Climate Factors
Elevation significantly alters the climate, setting high deserts apart from low-lying arid zones like the Sahara. High deserts experience a much greater diurnal temperature range, meaning the difference between daytime highs and nighttime lows is pronounced. Thinner air at higher altitudes is less effective at trapping heat, allowing the ground to warm rapidly during the day and lose heat quickly after sunset.
The most defining climatic feature is the significantly colder winter season, where sub-freezing temperatures and snow are common occurrences. High elevation also leads to increased exposure to solar radiation because the atmosphere is less dense. Combined with strong, drying winds often funneled across high plateaus, the environment presents extreme thermal and desiccating stress.
Unique Ecological Adaptations
Life in the high desert must cope with the dual challenge of aridity and extreme temperature fluctuations, leading to specialized survival strategies in both flora and fauna. Plants, such as the Creosote bush and various sagebrush species, often possess deep taproots to reach distant groundwater. They also utilize a dense network of shallow roots to absorb infrequent surface moisture, and many have small, waxy, or hair-covered leaves to minimize transpiration and reflect intense solar radiation.
Animals employ behavioral adaptations to survive the cold winters and daily temperature swings. Many small mammals, such as the kangaroo rat, are nocturnal and spend the day in temperature-stable burrows. Some species enter a state of torpor or hibernation during the coldest months to conserve energy, while others can produce highly concentrated urine to drastically reduce water loss.
Major Geographical Examples
Several regions around the world exemplify the high desert classification, illustrating the impact of elevation on arid ecosystems. The Great Basin Desert in the western United States is a prominent example, spanning much of Nevada with elevations generally ranging from 3,000 to 6,000 feet. Much of the Mojave Desert, particularly the western portion, is also considered high desert, typically lying between 2,000 and 4,000 feet.
On a global scale, the Patagonian Steppe in South America and the intermountain plateaus of Central Asia, such as the Gobi Desert, also fit this description, often existing in high-altitude rain shadows. The Atacama Desert in Chile features plateaus at an average elevation of nearly 13,000 feet, making it one of the highest arid zones on Earth. These geographically diverse examples are united by the combination of a dry climate and significant altitude.