drylands

Drylands are regions where rainfall is too low or erratic to meet the long-term water needs of vegetation and people. They cover about 40% of the Earth's land area and host a substantial portion of the world’s population, particularly in Africa, Asia, and parts of the Americas. Drylands include deserts, semi-arid steppes, and dry sub-humid zones, with persistent water scarcity.

The aridity index, defined as precipitation divided by potential evapotranspiration, classifies zones as arid (<0.2), semi-arid (0.2–0.5), and dry sub-humid (0.5–0.65). Rainfall is low and highly seasonal, and temperatures can be extreme.

Vegetation is typically sparse and drought-adapted, including grasses, shrubs, and drought-tolerant trees. Soils are varied but can be shallow or rocky and are prone to erosion and salinization under disturbance. Biodiversity includes specialized species and habitats that support pastoralism and mixed cropping in some areas.

Human populations rely on rainfed agriculture and grazing, making drylands vulnerable to drought, land degradation, and climate change. Sustainable land management—water harvesting, soil conservation, rangeland management, and diversified livelihoods—aims to bolster resilience. International initiatives such as the UN Convention to Combat Desertification address cross-border challenges and knowledge sharing.