Geography Drought
Woonsup Choi
  • LAST REVIEWED: 25 September 2023
  • LAST MODIFIED: 25 September 2023
  • DOI: 10.1093/obo/9780199874002-0215


Drought is a natural disaster that has plagued human society throughout history. However, the meaning of drought varies by perspective and academic discipline, and the cause of drought is difficult to pinpoint. Despite the variation in its meaning, drought generally refers to the condition of an abnormally low amount of water for a given climate. Here the water can be precipitation, streamflow, soil moisture, groundwater, reservoir storage, and the like, but the lack of precipitation is a precursor for other types of drought. The lack of precipitation is often associated with anomalous atmospheric conditions such as atmospheric-circulation anomalies, higher-than-normal temperatures, and lower-than-normal relative humidity. Sea surface temperature anomalies may lead to sustained atmospheric-circulation anomalies. Drought defined as a lack of precipitation is often called meteorological or climatological drought. Other drought types can be classified within the context of the affected sectors, such as agricultural, hydrological, and socioeconomic drought. Agricultural drought generally refers to a lack of soil moisture, and hydrological drought refers to a lack of surface and subsurface water (e.g., streamflow and groundwater). Socioeconomic drought hampers human activities such as industry or water supply. As meteorological drought persists, other types of drought can follow. Such definitions of drought are regarded as conceptual definitions, but operational ones are also necessary for quantitative understanding and management of drought events. Operational definitions use quantitative indices to identify the occurrence and characteristics of drought events such as onset, duration, termination, deficit volume, and spatial extent of drought. Much of existing drought research concerns developing, revising, and applying drought indices to investigate spatial and temporal patterns of drought at various geographical scales. Drought research has progressed along several directions, such as causes and drivers of drought, characteristics of drought events, impacts, and mitigation. Each of these directions is represented by the works cited in this article.

Key Publications

One of the most important issues in drought research is how to conceptualize and define droughts. Cook 2019, Wilhite and Glantz 1985, and Mishra and Singh 2010 offer a review of drought concepts, definitions, classification, and indices, and Robeson 2008 reviews research topics in drought that are relevant to applied climatology. There are numerous quantitative indices of drought, and the PDSI (Palmer Drought Severity Index) developed in Palmer 1965 and the SPI (Standardized Precipitation Index) developed in McKee, et al. 1993 are widely used as operational definitions of meteorological drought. The authors of Byun and Wilhite 1999 developed the EDI (Effective Drought Index) while criticizing SPI. Yevyevich 1967 suggests a threshold-level approach to defining hydrological droughts. Van Loon 2015 offers a comprehensive review of hydrological drought, and Van Loon, et al. 2016 reframes the approach to drought with regard to human activities. Tallaksen and van Lanen 2004 collects chapters in various aspects of drought in streamflow and groundwater.

  • Byun, Hi-Ryong, and Donald A. Wilhite. “Objective Quantification of Drought Severity and Duration.” Journal of Climate 12.9 (1999): 2747–2756.

    DOI: 10.1175/1520-0442(1999)012<2747:OQODSA>2.0.CO;2

    Discusses major existing drought indices and proposes EDI, which diagnoses meteorological drought by using daily precipitation while giving more weight to recent precipitation than precipitation more distant in the past. An authoritative reference for EDI.

  • Cook, Benjamin I. Drought: An Interdisciplinary Perspective. New York: Columbia University Press, 2019.

    DOI: 10.7312/cook17688

    A comprehensive and concise volume that explains drought in various perspectives, including hydroclimatology, climate change, land management, and groundwater. One of the best introductions for those who pursue scientific understanding of drought and good as an undergraduate-level textbook.

  • McKee, Thomas B., Nolan J. Doesken, and John Kleist. “The Relationship of Drought Frequency and Duration to Time Scales.” Proceedings of the 8th Conference on Applied Climatology 7.22 (1993): 179–183.

    Defines drought on the basis of standardized precipitation, which is the difference between precipitation for a particular period and the mean divided by the standard deviation. The mean and standard deviation are determined from historical data. The standardized precipitation is expressed as SPI for varying lengths; for example, one month (SPI-1), three months (SPI-3), twelve months (SPI-12), etc. A common reference for SPI.

  • Mishra, Ashok K., and Vijay P. Singh. “A Review of Drought Concepts.” Journal of Hydrology 391.1–2 (2010): 202–216.

    DOI: 10.1016/j.jhydrol.2010.07.012

    Reviews a wide range of issues related to drought, including need for drought research, drought definitions and classification, drought indices, and relationship between drought and large-scale climate indices. One of the best introductions for those who pursue scientific understanding of drought.

  • Palmer, Wayne C. Meteorological Drought. Washington, DC: US Department of Commerce, 1965.

    An authoritative reference for PDSI. Defines drought severity and duration, considering water balance components as well as precipitation. The PDSI numbers are classified by levels of dryness and wetness.

  • Robeson, Scott M. “Applied Climatology: Drought.” Progress in Physical Geography 32.3 (2008): 303–309.

    DOI: 10.1177/0309133308091951

    Reviews major research fields in drought from an applied-climatology perspective, focused on monitoring, climate change impacts, and modeling.

  • Tallaksen, Lena M., and Henny A. J. van Lanen, eds. Hydrological Drought: Processes and Estimation Methods for Streamflow and Groundwater. Amsterdam: Elsevier, 2004.

    A collection of chapters addressing drought in streamflow and groundwater. Chapters about the science or management of drought are adequate for entry-level graduate students, but those about drought estimation methods are highly technical.

  • Van Loon, Anne F. “Hydrological Drought Explained.” Wiley Interdisciplinary Reviews: Water 2.4 (2015): 359–392.

    DOI: 10.1002/wat2.1085

    Provides a comprehensive review of hydrological drought, including typology and indices and discusses research gaps and challenges.

  • Van Loon, Anne F., Kerstin Stahl, Giuliano Di Baldassarre, et al. “Drought in a Human-Modified World: Reframing Drought Definitions, Understanding, and Analysis Approaches.” Hydrology and Earth System Sciences 20.9 (2016): 3631–3650.

    DOI: 10.5194/hess-20–3631–2016

    Emphasizes the impact of humans on drought, particularly hydrological drought, and reframes the way that drought is defined and analyzed in the Anthropocene. Clarifies drought terminology and identifies research gaps in drivers, modifiers, impacts, feedbacks, and baselines of drought.

  • Wilhite, Donald A., and Michael H. Glantz. “Understanding the Drought Phenomenon: The Role of Definitions.” Water International 10.3 (1985): 111–120.

    DOI: 10.1080/02508068508686328

    Provides detailed discussion of drought definitions. Suggests subdividing the definitions into four types on the basis of disciplinary perspectives (meteorological, agricultural, hydrological, and socioeconomic), and such a classification has been widely adopted in the literature, including the review in Mishra and Singh 2010.

  • Yevyevich, Vujica M. “An Objective Approach to Definitions and Investigations of Continental Hydrologic Droughts.” Hydrology Papers, Colorado State University 23 (1967).

    Suggests an “objective” definition of hydrological droughts at continental or large-area scales. It is regarded as the first work that defined droughts by using runs of the sequence of a variable, where droughts are defined in terms of duration, deficit volume, and intensity. Most papers investigating hydrological droughts cite this paper.

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