Deserts

Deserts are regions that receive limited precipitation, typically less than 250 millimeters of rain per year. In some definitions aridity also depends on potential evapotranspiration, with deserts defined as areas where evaporation exceeds precipitation for most of the year. Deserts cover about 20% of the Earth's land surface and occur on every continent, from hot subtropical zones to cold continental interiors and coastal basins.

Formation and climate: Deserts form where dry air descends at subtropical latitudes, where rain shadows block moist air, and in interior regions far from oceans. Coastal deserts arise where cold ocean currents limit evaporation and condensation. Hot deserts characteristically show high daytime temperatures and large diurnal swings; cold deserts have very low temperatures and often snow.

Ecology and adaptations: Plant life is typically sparse and drought-tolerant, including succulents, deep-rooted shrubs, and grasses. Animals—such as camels, fennec foxes, jerboas, lizards, and many insects—often conserve water, emerge at night, or burrow. Oases and seasonal rivers support higher productivity. Desert ecosystems are sensitive to disturbances and rely on irregular rainfall pulses.

Humans and threats: Humans have lived in deserts for millennia, adapting through nomadic herding, irrigation, and trade routes. Modern pressures include overuse of scarce water, mining, oil extraction, and land degradation. Climate change can intensify aridity and desertification, threatening biodiversity and livelihoods.

Notable deserts: Sahara, Arabian, Mojave, Sonoran, Kalahari, Namib, Gobi, and Great Basin. Polar deserts in Antarctica and parts of the Arctic are among the coldest and driest landscapes on Earth.