Drought and Water Scarcity
Drought is a temporary deficit of water relative to normal conditions, and water scarcity is a longer-term imbalance between demand and available supply; both threaten water security.
Definition
Drought is a sustained, naturally driven deficit of water (in precipitation, soil moisture, or streamflow) below normal conditions, while water scarcity is a persistent shortfall of available water relative to demand; both are characterized by their severity, duration, and extent.
Scope
This topic covers the definition and types of drought, the indices used to characterize and monitor it, low-flow hydrology, and the distinction between natural drought and human-driven water scarcity. It addresses the deficit end of the water balance, complementing flood hydrology and water-resources management.
Core questions
- How are droughts defined and classified?
- How are drought severity and onset measured with indices?
- How does drought propagate from rainfall to soil moisture to streamflow?
- How does natural drought differ from human-induced water scarcity?
Key concepts
- Meteorological, agricultural, hydrological drought
- Standardized Precipitation Index
- Drought severity, duration, extent
- Low-flow hydrology
- Drought propagation
- Water scarcity and water stress
Key theories
- Drought definitions and typology
- Wilhite and Glantz showed that drought has no single definition and is best classified into meteorological, agricultural, hydrological, and socioeconomic types, each with different indicators and impacts.
- Standardized drought indices
- Indices such as the Standardized Precipitation Index quantify drought severity over chosen timescales, enabling consistent monitoring, comparison, and triggering of drought response.
- Drought propagation
- A precipitation deficit propagates with delay and attenuation through soil moisture to groundwater and streamflow, so hydrological drought lags and is modulated by catchment storage relative to meteorological drought.
Clinical relevance
Drought and scarcity analysis supports early warning and monitoring, the design of reservoirs and supplies to withstand dry spells, the setting of restrictions and drought plans, and the assessment of how climate change and rising demand intensify water stress with consequences for agriculture, ecosystems, and society.
History
Recognition that drought is multifaceted led Wilhite and Glantz to a four-type classification in 1985; the Standardized Precipitation Index of 1993 standardized monitoring, and later work clarified how droughts propagate through the hydrological cycle and how human water use blurs the line between natural drought and scarcity.
Debates
- Natural drought versus human-induced scarcity
- There is discussion over how to distinguish climate-driven drought from scarcity caused or worsened by human water use, since abstraction and land-use change can create or intensify water shortages independently of rainfall deficits.
Key figures
- Donald A. Wilhite
- Thomas B. McKee
- Anne F. Van Loon
Related topics
Seminal works
- wilhite1985
- mckee1993
- vanloon2015
Frequently asked questions
- What is the difference between drought and water scarcity?
- Drought is a temporary, naturally driven deficit relative to normal conditions, whereas water scarcity is a longer-term or structural imbalance between demand and available supply; a region can be water-scarce even without drought, and drought worsens existing scarcity.
- Why are there so many types of drought?
- A rainfall deficit affects different parts of the water cycle at different times: it first shows as a meteorological drought, then as low soil moisture (agricultural), and later as low streamflow and groundwater (hydrological), each relevant to different users and managed with different indicators.