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Frequently asked questions about droughts.

What is a drought?

When does a drought begin?

Does a shortage of rain mean a drought will occur?

Where do droughts usually occur?

What can be done to solve water problems during periods of drought?

When has North Dakota experienced droughts?

 

What is a drought?

The definition of drought varies on the basis of the situation or area for which drought is being defined.  A simple definition of drought is a period of water shortage.  However, a period of water shortage can range from a few days or weeks for some crops to a few years for large reservoirs or ground-water aquifers.  Similarly, the water shortage can range from as little as an inch of precipitation for shallow root crops to as much as several feet of precipitation for water supplies that rely on streamflow or ground water.  Unlike the effects of other weather-related hazards, such as floods, the effect of a drought can develop slowly.

A drought is the result of many natural and human factors that affect the environment.  Matthai (1979, p. 5) stated that

"Among the natural factors are the climate of the area; antecedent conditions as exemplified by the amounts of soil moisture, rain, and snow; the distribution of rain and snow in time and space; water-table levels during the drought; water quality; and soil type.  Human factors include the degree of development of water storage and distribution systems; the number, location, and depths of wells; the patterns of water use and per capita consumption; the legal aspects relating to property rights, project operating rules, water-quality standards, and service contracts; economic considerations; and many more.  Therefore, a definition of a drought must be tailored to the conditions in an area at a given time."

The World Metrological Organization identified five general types of drought (Subrahmanyam, 1967):

  1. Meteorologic drought--defined only in terms of precipitation deficiencies, in absolute amounts, for a given period.

  2. Climatological drought--defined in terms of precipitation deficiencies, in percentages of normal values.

  3. Atmospheric drought--defined not only in terms of precipitation deficiencies but possibly in terms of temperature, humidity, or windspeed.

  4. Agricultural drought--defined principally in terms of soil moisture and plant behavior.

  5. Hydrologic drought--defined in terms of reduction of streamflow, reduction in lake or reservoir storage, and lowering of ground-water levels.

An additional type of drought, the water-management drought, was added by Matthai (1979) to characterize water-supply shortages caused by the failure of water-management practices or facilities, such as an integrated water-supply system and surface or subsurface storage, to bridge normal or abnormal dry periods and equalize the water supply throughout the year.  In general, drought can be defined as an interval of time, generally in months or years, when the water supply at a given location is consistently short of the expected climatic and hydrologic norm.

A drought can only be described fully by the depiction of its numerous climatic and hydrologic elements.  Therefore, indices have been developed to simplify and present the climatic and hydrologic information and to characterize a drought spatially and temporally as to its intensity, duration, and severity.  Each of the indices has a different description of water shortage.  Some commonly used indices are departure from normal precipitation, departure from normal temperature, the Palmer Drought Severity Index, accumulated departure from normal streamflow, low-streamflow frequency, changes in water storage, ground-water levels and rates of decline, and lake levels.  Redmond (1991) reviewed the desirable properties of indices and stated that

It is important to remember that one index cannot describe everything about the original data.  Indices are intended to serve as approximations to real-world phenomena.  Decisions regarding which information to retain and incorporate in to the index are governed by the way the index is expected to be used.  This point should always be borne in mind when using any summarized quantity."

Source:  Williams-Sether, Tara, Macek-Rowland, K.M., and Emerson, D.G., 1994, Climatic and hydrologic aspects of the 1988-92 drought and the effect on people and resources of North Dakota: North Dakota State Water Commission Water Resources Investigation 29, 57 p.

References

Matthai, H.F., 1979, Hydrologic and human aspects of the 1976-77 drought: U.S. Geological Survey Professional Paper 1130, 84 p.

Redmond, Kelly, 1991, Climate monitoring and indices, in Wilhite, D.A., Wood, D.A., and Kay, P.A., eds., Drought management and planning: International Drought Information Center, Department of Agricultural Meteorology, University of Nebraska-Lincoln, IDIC Technical Report Series 91-1, p. 29-33.

Subrahmanyam, V.P., 1967, Incidence and spread of continental drought: World Meteorological Organization, International Hydrological Decade, Reports on WMO/IHD Projects, no. 2, Geneva, Switzerland.

 

When does a drought begin?

The beginning of a drought is difficult to determine. Several weeks, months, or even years may pass before people know that a drought is occurring, and dry periods can last for 10 years or more. During the 1930's, most of the United States was much drier than normal. In California, the drought extended from 1928 to 1937, and in Missouri, the drought extended from 1930 to 1941.  The extended dry period produced the "Dust Bowl" of the 1930's when dust storms destroyed crops and farms.

The first evidence of drought usually is seen in records of rainfall. Within a short period of time, the amount of moisture in soils can begin to decrease. The effects of a drought on flow in streams and rivers or on water levels in lakes and reservoirs may not be noticed for several weeks or months. Water levels in wells may not reflect a shortage of rainfall for a year or more after a drought begins.

Source:  Moreland, Joe A., 1993, Drought: U.S. Geological Survey Open File Report 93-642, 2 p.

 

Does a shortage of rain mean a drought will occur?

A period of below-normal rainfall does not necessarily result in drought conditions. Some rain returns to the air as water vapor when water evaporates from water surfaces and from moist soil. Plant roots draw some of the moisture from the soil and return it to the air through a process called transpiration. The total amount of water returned to the air by these processes is called evapotranspiration. Sunlight, humidity, temperature, and wind affect the rate of evapotranspiration. When evapotranspiration rates are large, soils can lose moisture and dry conditions can develop. During cool, cloudy weather, evapotranspiration rates may be small enough to offset periods of below-normal precipitation and a drought may be less severe or may not develop at all.

Source:  Moreland, Joe A., 1993, Drought: U.S. Geological Survey Open File Report 93-642, 2 p.

 

Where do droughts usually occur?

Some areas of the United States are more likely to have droughts than other areas. In humid, or wet, regions, a drought of a few weeks is quickly reflected in a decrease in soil moisture and in declining flow in streams. People who use water from streams in these areas may face water shortages as soon as streamflow begins to decline. In arid, or dry, regions, people rely on ground water and water in reservoirs to supply their needs. They are protected from short-term droughts but may have severe problems during long dry periods because they may have no other water source if wells or reservoirs go dry.

Source:  Moreland, Joe A., 1993, Drought: U.S. Geological Survey Open File Report 93-642, 2 p.

 

What can be done to solve water problems during periods of drought?

When droughts occur, there is not enough water to supply all needs. If water is diverted from streams to irrigate crops, streamflow will decrease. Reservoirs that may already be at low levels will be drawn even lower to supply water for power generation, to supply water to downstream cities and towns, or to maintain river levels high enough for navigation. Decreasing water levels in rivers, lakes, and reservoirs may cause problems for fish and wildlife that depend on wetlands or water bodies to survive.

Balancing the needs of all the users of a water supply during a drought can be very difficult. Local, State, and Federal agencies must make decisions on how water will be used to satisfy the most critical needs and to reduce economic and environmental problems. In times of severe drought, water users must cooperate and share the limited amount of water available to protect the critical needs of people, fish and wildlife, agriculture, and industry.

Conserving water is very important during periods of drought. Water saved by one user may be enough to protect the critical needs of others. Irrigation practices can be changed to use less water or crops that use less water can be planted. Cities and towns can ration water, factories can change manufacturing methods, and individuals can practice water-saving measures to reduce consumption. If everyone reduces water use during a drought, more water will be available to share

Source:  Moreland, Joe A., 1993, Drought: U.S. Geological Survey Open File Report 93-642, 2 p.

 

When has North Dakota experienced droughts?

Date-Area Affected-Recurrence Interval-Remarks

1885-86-Western part of State-Unknown-Especially severe in 1886; crops poor.

1929-42-Statewide-25 to 74 years-Regional drought.

1952-62-Statewide-26 to 50 years-Less-than-normal runoff in several consecutive years.

1972-77-James River and Beaver Creek-5 to 58 years-Localized drought in south-central part of State.

1980-81-Parts of the Red River of the North and Missouri and James River Basins-5 to 58 years-Less-than-normal runoff for 2 years.

1988-92-Statewide-19 to 54 years-Warm, dry conditions that resulted in less-than-normal streamflow across the State.

Data Source:

Ryan, G.L., Klapprod, L.A., 1991, North Dakota floods and droughts: U.S. Geological Survey Water-Supply Paper 2375, p. 435-442.

Williams-Sether, Tara, Macek-Rowland, K.M., and Emerson, D.G., 1994, Climatic and hydrologic aspects of the 1988-92 drought and the effect on people and resources of North Dakota: North Dakota State Water Commission Water Resources Investigation 29, 57 p.

Williams-Sether, Tara, 1999, From dry to wet, 1988-97, North Dakota: U.S. Geological Survey Fact Sheet FS-075-99, 4 p.