aridzone

An arid zone is a geographic region defined by persistent dryness, where annual precipitation is insufficient to meet the atmospheric demand for moisture. In climate science, aridity is typically expressed using an aridity or dryness index, such as the ratio of precipitation to potential evapotranspiration. Arid zones cover roughly one-third of Earth's land surface and include true deserts as well as semi-arid areas. They are found in subtropical latitude bands, high plateaus, interior of continents, and rain-shadow regions.

Climate and geography: Rainfall is infrequent and unpredictable; most precipitation occurs during short wet seasons or sporadic events. Evaporation exceeds rainfall for most of the year, producing large water deficits. Temperatures can be extreme, with hot days and cold nights; desert climates are classified as BWh or BWk and semi-arid as BSh or BSk in Köppen classification.

Ecosystems: Flora are drought-tolerant, with many succulent species, deep-rooted shrubs, or annuals with rapid life cycles. Fauna include small mammals, reptiles, and birds adapted to heat and scarcity; some species migrate or use nocturnal activity. Soils are often sandy or rocky, with high salinity in some zones; biological soil crusts may stabilize surfaces.

Human use and challenges: Arid zones support pastoralism, oases, and limited agriculture with irrigation, but water scarcity constrains development. Climate change is altering precipitation patterns and increasing aridity in some regions, contributing to desertification and land degradation. Conservation and sustainable management focus on water efficiency, rangeland management, and protecting biodiversity.