2012-2016 California Drought: Historical Perspective
Nov 29, 2017 at 2:00pm
Staff, USGS – California Water Science Center
The most recent drought spanned water years 2012 through 2016 - it is timely to compare it with other historic California droughts and consider some of the lingering impacts.
On January 17, 2014, California State Governor Jerry Brown declared a drought state of emergency. On April 2, 2017, Governor Brown lifted the drought emergency, but declared that California must continue water conservation efforts. With the official conclusion of the most recent drought, which spanned water years 2012 through 2016, it is timely to compare it with other historic California droughts and also to consider some of the lingering impacts.
Water year is defined as starting on October 1 of the preceding year and ending on September 30 of the water year (e.g. Water Year 2017 starts on October 1, 2016, and ends on September 30, 2017). Hydrologically, “water year” is a useful metric because the majority of precipitation in Western states occurs from late fall to early summer. Thus, water years are useful to delineate dry and wet periods.
California's Historic Droughts
Drought is a prolonged and widespread deficit in available water supplies that may cause substantial economic or social impacts, or physical damage or injury to individuals, property, or the environment. These prolonged periods may include one or more years of near normal precipitation, if significant drought impacts continue during this time period. Considering this definition, droughts in California can be classified in four ways:
- Meteorological drought is a period of one, or more water years, of below-normal precipitation;
- Hydrological drought is a period of one, or more water years, in which there is below-normal availability of surface water and groundwater;
- Agricultural drought is a period of one, or more water years, in which water available for agricultural production is curtailed by 25% or more; and
- Ecological drought is a period of one, or more water years, during which deficits in natural water availability create multiple stressors across ecosystems.
Since 1895, there have been six prolonged dry periods lasting two years or longer, which qualify as droughts under all of the above drought classifications. They are: water years (WY) 1928-34, WY 1976-77, WY 1987-92, WY 2001-02, WY 2007-09 and WY 2012-16. The impacts from a drought are a function of both duration and severity (or average annual deficits). Shorter timeframe droughts were included either because of their severity, such as the WY 1976-77 drought, or their impacts, such as the reduced hydroelectric power production which contributed to the Western Energy Crisis of 2001-02. The longer the duration of a drought, even under less severe cumulative annual deficits, generally, the worse the impacts.
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