WSP04710

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 6/1/1997
• Author: Donald Wilhite
• Title: Improving Drought Management in the West
• Water Supply Pro - Doc Type: Report/Study

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The Concepl of Droughl

Because drought affects so many economic and social sectors, scores of
drought definitions have been developed by a variety of disciplines. In
addition, because drought occurs with varying frequency in nearly all regions
of the globe, in all types of economic systems, and in developing and developed
countries alike, the approaches taken to define it should be impact and region
specific. The lack of a precise and objective definition in specific situations
has been an obstacle to understanding drought, which has led to indecision
and/or inaction on the part of managers, policymakers, and others. It must be
accepted that the importance of drought lies in its impacts,

Drought has been grouped by type as follows: meteorological, agricultural,
hydrological, and socioeconomic (Wilhite and Glantz, 1985). Meteorological
drought is expressed solely on the basis of the degree of dryness (often in
comparison to some "nonnal" or average amount) and the duration of the dry
period. Definitions of meteorological drought must be considered as region
specific, since the atmospheric conditions that result in deficiencies of
precipitation are highly variable from region to region. Agricultural drought
specifically concerns the effects of water shortages on crops and grasses and
other forages. Therefore, agricultural drought is most closely associated with
deficiencies that occur in soil moisture and lead to losses in yield. Agriculture
is usually the first sector to experience the devastating effects of drought.
Hydrological droughts are concerned more with the effects of periods
of precipitation shortfalls on surface or subsurface water supply
(i.e., streamflow, reservoir and lake levels, groundwater) rather than with
precipitation shortfalls. Hydrological droughts are usually out of phase with
meteorological and agricultural droughts. Water in hydrologic storage
systems (e.g., reservoirs, rivers) is often used for multiple and competing
purposes, further complicating the sequence and quantification of impacts.
Competition for water in these storage systems escalates during drought, and
conflicts between water users increase significantly. Because regions are
interconnected by hydrologic systems, drought occurring upstream may result
in serious impacts downstream as surface and subsurface water supplies are
affected, even though downstream areas may not be experiencing meteor-
ological drought, Upstream changes in land use (e.g., deforestation, changes
in cropping patterns) may alter runoff and soil infiltration rates, which may
affect the frequency and severity of droughts downstream.

Finally, socioeconomic drought associates the supply of and demand for some
economic good with elements of meteorological, agricultural, and hydrological

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