BWh

BWh is a designation in the Köppen climate classification for hot desert climates. It characterizes arid regions where the average annual temperature is at least 18°C, and precipitation is very limited. In these areas, years with drought are common and rainfall, when it occurs, is infrequent and irregular.

Climate characteristics of BWh include very high daytime temperatures, especially in the hot season, and substantial diurnal temperature variation. Winters, while milder than summers, can still be warm. Along with low rainfall, high evaporation rates drive dryness. The result is sparse vegetation and soils that are often sandy or rocky, with limited soil moisture available for sustained plant growth. In many BWh regions, humidity is low and dust events can occur.

Geographically, BWh climates are associated with subtropical desert belts and can be found in large desert regions of Africa, the Middle East, parts of Central and South Asia, and in interior and downwind areas of large continents. Distinct microclimates occur near oases, coastlines, or mountains, where local conditions moderate temperatures or increase precipitation slightly.

Ecology and human activity in BWh areas reflect water scarcity and heat stress. Flora is typically xerophytic, with deep-rooted, drought-tolerant species, while fauna include heat-adapted mammals, reptiles, and many insects. Human populations tend to cluster around reliable water sources, such as oases or groundwater basins, and economic activity often relies on irrigation, mining, or energy resources. Climate change may alter precipitation patterns and exacerbate aridity in some regions.

See also: Köppen climate classification, desert climates, arid land ecosystems.