Origins
The word 'drought' descends from Old English 'drΕ«gaΓΎ' or 'drΕ«goΓΎ,' meaning 'dryness' or 'a period ofβββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ dry weather.' The Old English word derives from the verb 'drΕ«gian' (to dry up, to wither), from Proto-Germanic *draugiz (dry), which also produced Old English 'drΘ³ge' (dry) β the direct ancestor of modern English 'dry.' The deeper root is PIE *dhreugh-, meaning 'dry,' 'firm,' or 'solid,' with an underlying sense of the absence of moisture.
The PIE root *dhreugh- generated a remarkably interconnected English word family. 'Dry' (the adjective) is the most direct descendant. 'Drought' adds the abstract suffix '-th' (as in 'growth,' 'warmth,' 'health') to form 'dry-ness.' 'Drain' (to remove water, to make dry) is from the same root. Most surprisingly, 'drink' and 'drench' are also related: the original semantic connection is that drinking is the act of remedying dryness β to drink is to answer the state of being dry. The word 'drench' originally meant 'to cause to drink' (to drench an animal was to force it to swallow liquid medicine), and only later shifted to mean 'to soak thoroughly.' The apparent paradox of 'dry' and 'drink' sharing a root dissolves when we see that the root's core meaning was the condition of dryness, and all the other words describe responses to or aspects of that condition.
The spelling of 'drought' has been unstable throughout English history. Middle English forms include 'droughte,' 'drouthe,' 'druthe,' and 'drouth.' The form 'drouth' (rhyming with 'mouth') survived in dialectal and literary use into the twentieth century β it appears in Robert Burns and in American regional speech. The standard modern form 'drought' (rhyming with 'out') won out in standard English, but the pronunciation has shifted: the Old English 'drΕ«gaΓΎ' had a long 'oo' sound, which diphthongized during the Great Vowel Shift.
Development
Drought has been one of the most consequential phenomena in human history. The collapse of the Akkadian Empire (c. 2154 BCE), the decline of the Old Kingdom of Egypt, the abandonment of Ancestral Puebloan settlements in the American Southwest (the great drought of 1276β1299), the Irish famine of 1740β1741, and the Dust Bowl of the 1930s were all driven or exacerbated by drought. Climate scientists using tree-ring data (dendroclimatology) have identified 'megadroughts' in the American West lasting decades β far longer than anything in the modern record.
The figurative use of 'drought' to mean any prolonged absence or scarcity dates from the sixteenth century. A 'drought of ideas,' a 'scoring drought' in sports, and similar usages exploit the metaphor of dryness as absence. In cricket, a batsman who has not scored runs for an extended period is said to be enduring a 'drought.'
The scientific classification of drought is more complex than the popular understanding. Meteorological drought is simply below-normal precipitation. Agricultural drought occurs when soil moisture falls below the level needed for crops. Hydrological drought refers to depleted surface and groundwater. Socioeconomic drought occurs when water shortages affect human activity. A region can experience agricultural drought without meteorological drought (if temperatures are unusually high, evapotranspiration increases) and vice versa. The Palmer Drought Severity Index (PDSI), developed in 1965, attempts to standardize drought measurement, but drought remains one of the most difficult natural hazards to define precisely because its severity depends on duration, intensity, spatial extent, and the demands placed on the water supply.