Deserts and Semiarid Regions: Understanding the Aridity Gradient

Precipitation Gradient

• Deserts: < 250 mm (10 in) annual rainfall.
• Semiarid: 250–750 mm (10–30 in) annually.

Transition Zones

Semiarid regions border deserts, experiencing periodic droughts and mixed vegetation (drought-tolerant grasses, shrubs).

Shared Climate Traits

High temperatures, low humidity, limited cloud cover, intense solar radiation.

Vegetation & Soils

• Sparse, xerophytic plants in deserts; more grasses/shrubs in semiarid zones.
• Soils low in organic matter, coarse (sand/gravel), nutrient-poor.

Human Habitation

Both pose challenges (water scarcity, heat), but semiarid areas can support irrigated agriculture.

Global Distribution

Found in rain shadows, subtropical highs, continental interiors (e.g., Sahara/Sahel, Gobi/Steppe, Chihuahuan/Sonoran margins).