Aridification

Aridification is the long-term process by which a region becomes drier, through declining precipitation, rising evaporative demand, or both.

Precipitation: Water released from the atmosphere that reaches Earth’s surface as rain, snow, sleet, or hail. A sustained decline in precipitation can reduce a region’s water supply.
Aridity: The persistent climatic condition of low water availability, commonly assessed by comparing precipitation with atmospheric evaporative demand. Aridity describes the dry climate state that aridification can produce.
Paleoclimatology: The study of past climates using evidence preserved in natural archives and historical records. Long records help distinguish persistent aridification from short-lived drought.
Hydrological cycle: The continuous movement of water among the atmosphere, land, oceans, and living organisms. Aridification alters regional flows and storage within the larger water cycle.
Potential evapotranspiration: The rate at which water could evaporate and plants could transpire given available energy and atmospheric demand. Rising atmospheric demand can intensify drying even without less rainfall.
Drought: A temporary period of unusually low water availability relative to a region’s normal conditions. Drought is a temporary anomaly; aridification is a long-term shift.
Paleosol: A former soil preserved within a sedimentary sequence, recording conditions during its formation. Soil features can preserve evidence of past shifts toward drier environments.
Ecological succession: The gradual change in an ecological community’s composition and structure over time. As conditions dry, plant and animal communities may shift toward drought-tolerant forms.
Hadley circulation: A tropical atmospheric circulation in which air rises near the equator and descends in the subtropics. Shifts in its descending dry-air belt can alter subtropical rainfall.
Aridity index: A measure of climatic dryness based on the relationship between precipitation and potential evapotranspiration. It provides a common way to quantify changing climatic dryness.

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