Drought and Drought Response Introduction
The word “drought” is a relative term, and is defined differently by different regions and sources. Webster’s Dictionary defines drought as “a long period of no rain”; though this is an inadequate definition for the water supply industry. Wikipedia describes drought in stages and effects: “As a drought persists, the conditions surrounding it gradually worsen and its impact on the local population gradually increases. Droughts go through three stages before their ultimate cessation.
- Meteorological drought is brought about when there is a prolonged period with less than average precipitation. Meteorological drought usually precedes the other kinds of drought.
- Agricultural droughts are droughts that affect crop production or the ecology of the range. This condition can also arise independently from any change in precipitation levels when soil conditions and erosion triggered by poorly planned agricultural endeavors cause a shortfall in water available to the crops. However, in a traditional drought, it is caused by an extended period of below average precipitation.
- Hydrological drought is brought about when the water reserves available in sources such as aquifers, lakes and reservoirs falls below the statistical average. Like an agricultural drought, this can be triggered by more than just a loss of rainfall.”
As used in the water industry, "drought" is a subjective and relative term. In most of the arid regions of Western states, seven months of no rainfall (March through October) would not be labeled as a drought. In the Midwestern states, as few as seven weeks without rain could be considered a drought. Similarly, an annual rainfall of 25 inches would be considered a wet year in Mesa Arizona; and considered a severe drought in Waterloo Illinois. In addition, the water supply of many western states is more dependent on snowfall in mountain ranges located hundreds of miles away, than the local rainfall. Drought conditions and appropriate response is specific to a region and the local conditions. Below are a few examples of different drought definitions used in different locations.
South Carolina Department of Natural Resources (official state web site):
“Drought is a period of time with less-than-normal rainfall. No region, including South Carolina, is immune to the possibility of drought. Droughts are naturally occurring events. It is often difficult to determine when a drought has begun or ended. The seriousness of a drought depends upon geographic location, weather patterns, soils, water use patterns, and overall water quantity. The greater the demands placed on an area's water resources, the more serious the drought. Recovery from drought may take months or sometimes years of above average precipitation. There are different kinds of drought. A meteorological drought occurs when precipitation consistently falls short of average levels for periods of months or years. A hydrological drought occurs when the amount of water needed by crops for growth exceeds the amount available in the soil.”
California Department of Water Resources, Urban Drought Guidebook:
“In the most general sense, drought is 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. A water shortage occurs when supply is reduced to a level that cannot support existing demands. Natural forces, system component failure or interruption, or regulatory actions may cause these water shortages. Such conditions could last two to three months or extend over many years.”
City of Phoenix Arizona (official city web site):
“Though definitions vary, drought is generally interpreted as a set of complex physical and sociological influences over a large geographical area. It is not a distinct event, such as a hurricane, a fire, or a flood, but a combination of many coincidental factors working together over a period of time. In simple terms, a drought occurs when water supplies cannot meet established demands for a period of time that cannot be defined.
In its broadest sense, drought can be caused by seasonal or multi-year weather conditions, a curtailment of delivery from raw water suppliers because of water quantity or quality problems, a supply deficiency due to water supply system structural failure, or any of a number of natural or man-made situations. A supply insufficiency occurs when the water available in an area is not sufficient to meet immediate unrestricted demand. While drought is usually systemic and regional in nature and of indeterminable length, a supply insufficiency may be system-wide or very localized, can be of relatively short duration, and may be caused by unforeseen increases in water demand or failure of a localized part of the storage or delivery system to provide a sufficient unrestricted supply of water.”
To most water suppliers, a drought is defined as much by the demand for the water as by the availability of water. Rainfall or lack thereof is no longer the sole factor is declaring a drought. Some droughts are caused by unusual demand increases even when the water supply is at normal levels such as: hot dry summers causing increased irrigation needs. Whatever the reasons for the drought, the water supplier must take action to mitigate the effects of the water shortage and assure a reliable water supply is available to meet the health and safety needs of the community.
"And it never failed that during the dry years the people
forgot about the rich years, and during the wet years they lost all memory of the dry years. It was always that way."
- John Steinbeck, East of Eden
When drought occurs, the water supplier and community must take action to reduce the demand for water. While increasing water supplies would be of benefit, most such remedies require more than 5 years to plan and construct new reservoirs, canals, and/or groundwater sources. Reducing water demand can result in significant positive effects within only a few days. A drought response plan can be implemented where good pre-planning has already laid the groundwork for actions.
It is important to prepare a drought response plan before a drought occurs. This allows time for the plan to receive public review and comment while not in a crisis mode. Contingency planning before a shortage allows selection of appropriate responses consistent with the varying severity of shortages. Most water utilities and communities define different stages (severity) of drought, and appropriate action for each stage. Public outreach and education programs should be prepared in advance, with printed materials readily available for distribution.
Voluntary action from water users can result in up to 25% water use reduction for short periods of time. Mandatory restrictions have resulted in as much as a 40% reduction of water use. This savings effect is directly related to: a) the public’s belief that the emergency is real; b) the public clearly understands the actions required to reduce water use; and c) the active enforcement of mandatory water use restrictions. It is very important for water suppliers to understand the public seldom sustains the voluntary water conservation levels more than a few months. Drought response actions, even mandatory water use restrictions are designed to be suspended once the drought is deemed over. Drought response programs and water efficiency programs are two very different actions for two different problems.
Water efficiency programs are designed to effect long-term (even permanent) water use reductions; drought response is designed to solve short term water supply deficits. Water efficiency programs can reduce the impact of subsequent droughts, but water efficiency strategies continue beyond the term of a drought. Water efficiency planning is usually based on the economics of avoided costs or least cost planning. Drought response is meant to solve an emergency supply shortfall; thus, does not always need to be justified by avoided costs.
Drought Guidance and Resources
California Department of Water Resources provides and excellent guidebook for drought planning and mitigation. You can view and download a copy of their 2008 Urban Drought Guidebook here. Additionally, a March 2010 update has been released and is available for download - CA 2010 Drought Report Update.
The National Drought Mitigation Center at the University of Nebraska was established in 1995 and offers updated information on drought conditions, planning, and response actions. The National Drought Mitigation Center hosts the U.S. Drought Monitor which releases updated drought maps on a weekly basis each Thursday.
The 2003 GAO report on freshwater supply and states' view on potential federal assistance in times of shortage.
California 20x2020 Draft Water Conservation Plan (April 2009)
Association of California Water Agencies (ACWA) - California Drought - Actions Taken by Local Agencies
California Urban Water Conservation Council Drought Site