Arid climate

An arid climate has persistently low precipitation relative to potential evaporation and water demand, producing chronic moisture deficits.

Potential evapotranspiration: The rate at which water could evaporate and plants could transpire given available energy and moisture. Aridity depends on how precipitation compares with this atmospheric demand for water.
Precipitation: Water falling from the atmosphere to Earth’s surface as rain, snow, sleet, or hail. Its scarcity is the defining water-input constraint in arid climates.
Dryland farming: Crop production in regions where rainfall is the main water source and irrigation is limited or absent. Its methods are adapted to the unreliable, low precipitation of arid settings.
Sahara: The vast desert region spanning much of North Africa. Its extreme dryness illustrates the subtropical desert climate at continental scale.
Aridity index: A ratio comparing precipitation with potential evapotranspiration to classify climatic dryness. This index turns the climate’s precipitation deficit into a measurable quantity.
Evaporation: The physical process by which liquid water becomes water vapor. High evaporative loss helps explain why modest rainfall may not relieve aridity.
Irrigation: The artificial application of water to soil or crops. It can support agriculture where precipitation alone cannot meet crop water demand.
Atacama Desert: A coastal desert in northern Chile known for exceptionally low precipitation. Cold ocean currents and rain-shadow effects combine to produce its severe aridity.
Hadley cell: A tropical atmospheric circulation cell in which air rises near the equator and descends in the subtropics. Its descending dry air helps create major belts of subtropical aridity.
Water balance: An accounting of water entering, leaving, and being stored within a system. Arid climates persist when climatic water inputs fail to meet losses and demand.

Linked from 47 pages