Droughts – Introduction

California Drought[3] [4] [5]
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Drought is referred to as a “creeping phenomenon” and its impacts vary from region to region. Drought can therefore be difficult for people to understand. It is equally difficult to define, because what may be considered a drought in one region may be different from another.[1]

In the most general sense, drought originates from a deficiency of precipitation over an extended period of time – usually a season or more – resulting in a water shortage for some activity, group, or environmental sector. Its impacts result from the interplay between the natural event (less precipitation than expected) and the demand people place on water supply, and human activities can exacerbate the impacts of drought. Because drought cannot be viewed solely as a physical phenomenon, it is usually defined both conceptually and operationally.[2]

Conceptual and Operational Definitions

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The conceptual definition, formulated in general terms, helps people understand the concept of drought. For example, drought in the conceptual view can be defined as:[6]

“a protracted period of deficient precipitation relative to the statistical multi-year average for a region.

The conceptual definition is important in establishing drought policy, which can incorporate an understanding of normal climate variability into its definition of drought.

Operational definitions help define the onset, severity, and end of droughts. No single operational definition of drought works in all circumstances, and this is a big part of why policy makers, resource planners, and others have more trouble recognizing and planning for drought than they do for other natural disasters.

An operational definition for agriculture might compare daily precipitation values to evapotranspiration rates to determine the rate of soil moisture depletion, then express these relationships in terms of drought effects on plant behavior (i.e., growth and yield) at various stages of crop development. A definition such as this one could be used in an operational assessment of drought severity and impacts by tracking meteorological variables, soil moisture, and crop conditions during the growing season, continually reevaluating the potential impact of these conditions.[7]


  1. NOAA – National Climatic Data Center – Definition of Drought: https://www.ncdc.noaa.gov/monitoring-references/dyk/drought-definition
  2. The National Drought Mitigation Center – What is Drought: http://drought.unl.edu/DroughtBasics/WhatisDrought.aspx
  3. Image Source: http://www.dot.gov/drought/drought2012 [Accessed January 22, 2014]
  4. California Department of Food and Agriculture – Drought:  http://www.cdfa.ca.gov/drought/
  5. California.gov – Drought Portal: http://ca.gov/drought/
  6. NASA Earth Observatory – Drought: The Creeping Disaster: http://earthobservatory.nasa.gov/Features/DroughtFacts/
  7. The National Drought Mitigation Center – What is Drought: http://drought.unl.edu/DroughtBasics/WhatisDrought.aspx