Drought

Drought is a prolonged period of unusually low precipitation that reduces water availability in ecosystems, agriculture, or human supplies. Its onset and severity depend on duration, local climate, and water demand.

Meteorological drought: A period when precipitation falls substantially below the local climatological average. This precipitation deficit is the basic atmospheric signal used to identify drought.
Standardized Precipitation Index: A drought index that expresses precipitation anomalies over selected time scales as standardized values. Its multiple time scales help distinguish short rainfall deficits from prolonged drought.
Agricultural drought: A soil-water shortage that limits crop growth or livestock production. It links depleted soil moisture to reduced harvests and agricultural losses.
Aridity: A long-term climatic condition of low water availability relative to atmospheric demand. Unlike drought, aridity describes a persistent climate rather than an unusual dry period.
Soil moisture: The water held in soil, available to plants and other processes. Rainfall shortages become agricultural stress when soil moisture declines.
Palmer Drought Severity Index: A water-balance-based index that estimates prolonged moisture deficits from precipitation and temperature. It offers a classic approach to assessing drought severity using supply and atmospheric demand.
Crop failure: The substantial loss of an expected harvest because crops die or produce poorly. Severe or poorly timed drought can prevent crops from completing growth.
Heat wave: A period of unusually high temperatures relative to a region’s climate. Heat can worsen drought through evaporation, but high temperatures alone are not drought.
Evapotranspiration: The combined transfer of water to the atmosphere through evaporation and plant transpiration. High atmospheric demand can intensify drought even when precipitation deficits are modest.
Drought monitoring: The systematic tracking of drought conditions using observations, indicators, and impact reports. Monitoring turns scattered weather and water data into timely assessments.

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