What is Drought?

Drought is a normal, recurrent feature of climate. It occurs almost everywhere, although its features vary from region to region. Defining drought is therefore difficult; it depends on differences in regions, needs, and disciplinary perspectives. Based on the many definitions that have appeared in the literature, for example, we might define drought in Libya as occurring when annual rainfall is less than 180 mm, but in Bali, drought might be considered to occur after a period of only 6 days without rain! In the most general sense, drought originates from a deficiency of precipitation over an extended period of time, resulting in a water shortage for some activity, group, or environmental sector. Whatever the definition, it is clear that drought cannot be viewed solely as a physical phenomenon.

What’s in this Section
This section provides an overview of drought—its definition and prediction, its history, and its relation to phenomena such as ENSO and the Greenhouse Effect—and climatology. Climographs for several U.S. cities and a series of historical Palmer Drought Severity Index maps are also in this section.

Understanding and Defining Drought
A discussion of the concept and definition of drought.
Drought Indices
An analysis and discussion of 8 drought indices, also available as a pdf.
Predicting Drought
The multiple causes of drought and their use in drought prediction.
Drought and Climate Change
A short history of the Greenhouse Effect and climate change.

What is Climatology?
A brief explanation.
Important Climatology Links and Paleoclimatology Links
Climographs of selected U.S. cities
Historical maps of the Palmer Drought Index
by U.S. climate division
Historical graphs of the Palmer Drought Index
by U.S. river basin

Drought in the Dust Bowl Years
A discussion of the impacts—social, environmental, and economic—of drought in the United States in the 1930s.

Understanding ENSO and Forecasting Drought
A discussion of El Niño’s impacts and its relationship to drought.
Reported Effects of the 1997 El Niño through October 30
An NDMC analysis of media reports.
Reported Drought-related Effects of the 1997–98 El Niño for November, December, January, February, March, April
An NDMC analysis of media reports. The April report contains a 6-month summary of El Niño’s worldwide effects.

Other Resources

©2002 National Drought Mitigation Center