A dry climate is one where the land loses more water to evaporation than it receives from rainfall. This simple imbalance, where water demand consistently outpaces water supply, is the defining feature that separates dry climates from all other climate types. Dry regions cover roughly 40% of Earth’s land surface (excluding Antarctica), making them the most widespread climate category on the planet.
How a Climate Qualifies as “Dry”
The key measurement isn’t just how much rain falls. It’s the relationship between precipitation and evapotranspiration, which is the total amount of water that evaporates from soil and gets released by plants. In a dry climate, evapotranspiration always exceeds precipitation. The air and ground are constantly pulling away more moisture than storms can replace.
This is why a place that gets 15 inches of rain per year might qualify as dry in a hot region but not in a cold one. Heat accelerates evaporation, so the same amount of rainfall goes much less far in a warm environment. The widely used Köppen climate classification system, which has been the global standard for over a century, accounts for this by factoring both temperature and precipitation into its formula for the “Group B” dry climate category.
Arid vs. Semi-Arid: Two Levels of Dryness
Dry climates break into two main types based on how extreme the moisture deficit is. Arid regions (true deserts) receive less than 10 inches (25 centimeters) of rain per year. Semi-arid regions (also called steppes) receive 10 to 20 inches (25 to 50 centimeters). Both lose more water to evaporation than they gain, but deserts lose it at more than twice the rate of incoming precipitation, while steppes have a somewhat narrower gap.
Each of these types also splits by temperature. Hot deserts and hot steppes sit at lower latitudes where average annual temperatures stay above 64°F (18°C) and frost is rare. Think of the Sahara or the Arabian Peninsula. Cold deserts and cold steppes occupy higher latitudes or elevations, with average temperatures below 64°F and winters that regularly dip below freezing. The Gobi Desert and the Great Basin of the western United States are cold desert examples, while the grasslands of Montana and Central Asia are classic cold steppes.
What Creates Dry Climates
Three main atmospheric and geographical mechanisms produce the world’s dry zones.
Subtropical high-pressure belts. Between roughly 20° and 40° latitude in both hemispheres, large masses of high-pressure air sit semi-permanently over the oceans. These systems are driven by the Hadley cell, a giant loop of atmospheric circulation near the equator. Air rises at the equator, travels poleward, then sinks back down in these subtropical zones. As it sinks, it compresses and warms, which makes it very effective at absorbing moisture rather than releasing it. This sinking air suppresses cloud formation and is the primary reason the world’s largest deserts cluster in these latitude bands.
Rain shadows. When moist air encounters a mountain range, it’s forced upward. As it rises, it cools, and cool air holds less moisture, so the water falls as rain or snow on the windward side. By the time the air crosses the peak and descends the other side, it has already dumped most of its moisture. The land on the sheltered, downwind side receives dramatically less rainfall. This is why eastern Washington state sits in near-desert conditions just a few hundred miles from one of the rainiest coastlines in North America.
Continental interiors. Locations far from any ocean simply don’t receive much moisture-laden air. Central Asia is the classic example: air masses lose their water content crossing thousands of miles of land before they ever arrive.
Wide Temperature Swings
One of the most noticeable features of dry climates is how much the temperature changes between day and night. Water vapor in the atmosphere acts like an insulating blanket, trapping heat after the sun goes down. In humid climates, nighttime temperatures stay relatively close to daytime highs. In dry climates, with very little atmospheric moisture, heat escapes rapidly after sunset. It’s common in desert regions for daytime temperatures to exceed 100°F while nighttime lows drop by 40 or 50 degrees.
Research published in the International Journal of Climatology found that this daily temperature range has actually been increasing in dry areas over recent decades, while it has been shrinking in wetter regions. The reason ties back to moisture: drier areas can’t increase their evaporation to buffer rising daytime highs, so maximum temperatures climb faster than minimum temperatures. In wetter areas, the opposite happens, with increased water vapor holding more heat overnight and narrowing the gap.
Soil in Dry Regions
The soils found in dry climates, known as aridisols, are fundamentally shaped by the lack of water moving through them. In wetter climates, rain constantly dissolves minerals and flushes them deep underground. In dry climates, there isn’t enough water to do this. Instead, minerals like calcium carbonate and gypsum accumulate in layers relatively close to the surface. Some dry soils also build up salts to levels that are toxic to most plants.
These soils typically have very thin organic layers on top because there’s limited plant life to drop leaves and roots into the ground. The U.S. Department of Agriculture defines aridisols as soils too dry for the growth of plants that need moderate moisture. In a typical year, these soils have no water available for plants for more than half the time that soil temperatures are warm enough to support growth.
How Plants Survive With Little Water
Plants in dry climates use two broad strategies: avoiding dehydration or tolerating it. Avoidance means finding ways to hold onto water or access hidden sources. Many desert plants grow extremely long tap roots that reach underground water supplies dozens of feet below the surface. Others have thick, waxy coatings on their leaves to slow water loss, or they curl their leaves during the hottest parts of the day to reduce exposure.
Cacti and succulents take avoidance to an extreme by storing water in their stems and opening their pores to absorb carbon dioxide only at night, when evaporation rates are lowest. Tolerance strategies work differently. Some plants essentially shut down during drought, entering a dormant state where they stop photosynthesizing and redirect their internal chemistry toward producing sugars and other molecules that protect their cells from drying out. When rain finally returns, they resume normal function.
A few remarkable species manage to stay active year-round in blistering conditions. Certain desert shrubs maintain high rates of photosynthesis even when leaf temperatures reach 109°F (43°C), relying on specialized forms of enzymes that remain functional at temperatures that would disable the same enzymes in temperate plants.
Where Dry Climates Are Found
The largest continuous dry zone on Earth stretches from the Sahara Desert across the Arabian Peninsula and into Central Asia. Other major dry regions include the interior of Australia, the Atacama Desert of South America (one of the driest places on the planet, with some weather stations having never recorded rain), the Kalahari and Namib deserts of southern Africa, and the Great Basin and Sonoran deserts of North America.
Semi-arid zones often ring the edges of true deserts, forming transitional bands. The Sahel region south of the Sahara, the grasslands of the American Great Plains, and the steppes of Central Asia all fit this pattern. These semi-arid zones are particularly sensitive to climate shifts because a small change in rainfall can push them toward either wetter or more desert-like conditions. Recent satellite studies indicate that global drylands have been expanding, now covering about 40% of Earth’s non-Antarctic land surface, an increase driven by shifting rainfall patterns and rising temperatures that accelerate evaporation.