Droughts in California
The historical and ongoing periodic droughts in California result from various complex meteorological phenomena, some of which are not fully understood by scientists.
Drought is generally defined as "a deficiency of precipitation over an extended period of time, resulting in a water shortage."
A lack of rainfall or precipitation in meager quantities, higher than average temperatures and dry air masses in the atmosphere commonly underlie drought conditions; these natural factors are further complicated by increases in populations and water demands. Since the California water supply is attained from numerous sources, fulfilled by varied and intricate weather patterns, there is no one cause of drought. California is not only the most populous state and largest agricultural producer in the United States, it is also the most biodiverse; as such, drought in California can have a far reaching economic and environmental impacts.
There are five major technical categories of drought: Meteorological, Agricultural, Hydrological, Socioeconomic, and Ecological. A meteorological drought may be short lived without causing disturbance; but when longer lasting may enter other categories according to its impacts. In addition to technical categories, Governor Gavin Newsom and his administration introduced in 2023 the concept of a political drought, where state public policy actions would need to continue even after short-term drought conditions may have ameliorated.
Precipitation in California occurs mostly from November to May, with the vast majority of rain and snowfall across the state occurring during the winter months. This delicate balance means that a dry rainy season can have lasting consequences.
Climate
Drought is intrinsic to the natural climate of California. Across the Californian region, paleoclimate records dating back more than 1,000 years show more significant dry periods compared to the latest century. Ancient data reveals two mega-droughts that endured for well over a century, one lasting 220 years and one for 140 years. The 20th century was fraught with numerous droughts, yet this era could be considered relatively "wet" compared against an expansive 3,500 year history. In recent times, droughts lasting five to 10 years have raised concern, but are not anomalous. Rather, decade long droughts are an ordinary feature of the state's innate climate. Based on scientific evidence, dry spells as severe as the mega-droughts detected from the distant past are likely to recur, even in absence of anthropogenic climate change.Climate change
According to the Intergovernmental Panel on Climate Change or IPCC, their Sixth Assessment Report on the effects of climate change revealed a number of scientifically supported claims on what is to become the future of the earth. While variability in climate patterns are a natural occurrence, AR6 concluded that human influences have increased the chance of compound extreme weather events, specifically "increases in the frequency of concurrent heatwaves and droughts on the global scale" with high confidence.According to the NOAA Drought Task Force report of 2014, the drought is not part of a long-term change in precipitation and was a symptom of the natural variability, although the record-high temperature that accompanied the recent drought may have been amplified due to human-induced global warming. This was confirmed by a 2015 scientific study which estimated that global warming "accounted for 8–27% of the observed drought anomaly in 2012–2014. Although natural variability dominates, anthropogenic warming has substantially increased the overall likelihood of extreme California droughts." A study published in 2016 found that the net effect of climate change has made agricultural droughts less likely, with the authors also stating that "Our results indicate that the current severe impacts of drought on California’s agricultural sector, its forests, and other plant ecosystems have not been substantially caused by long-term climate change."
Drought phases are integral to the climate of California. Furthermore, global La Niña or El Nino, or Neutral ENSO, meteorological events are generally associated with drier and hotter conditions and further exacerbation of droughts in California and the Southwestern and to some extent Southeastern United States. Meteorological scientists have observed that La Niñas have become more frequent over time.
Increasingly dramatic fluctuations in California weather have been observed in the 21st century. In 2015, California experienced its lowest snowpack in at least 500 years; the 2012–15 period was the driest in at least 1200 years. However, the winter of 2016–17 was the wettest ever recorded in Northern California, surpassing the previous record set in 1982–83. In February 2017, Shasta, Oroville and Folsom Lakes were simultaneously dumping water into the ocean for flood control. Lake Oroville flowed over the emergency spillway for the first time in 48 years, after the main spillway was damaged resulting in the temporary evacuation of 200,000 people. The combined inflow to Shasta, Oroville and Folsom Lakes on February 9 was. Two days later, the combined flood control release was. This water would have been worth $370M at Los Angeles County municipal rates.
Dry years
Throughout recent recorded history, California has experienced periodic droughts, such as 1841, 1864, 1895, 1924, 1928–1935, 1947–1950, 1959–1961, 1976–1977, 1986–1992, 2007–2009, and 2011–2017,2020–2022 and 2024-25.Since 1841, the following dry years have had significantly below-average precipitation.
- 1841
- 1863–1864
- 1895–1896
- 1917–1921
- 1922–1926
- 1928–1937
- 1943–1951
- 1959–1961
- 1971–1972
- 1976–1977
- 1987–1992
- 1999–2004
- 2006–2009
- 2011–2017
- 2020–2022
- 2024–2025
1841
1863–1864
This drought was preceded by the torrential floods of 1861–1862.1924
This drought encouraged farmers to start using irrigation more regularly. Because of the fluctuation in California weather, the need for consistent water availability was crucial for farmers.1928–1937
This drought occurred during the historical Dust Bowl period that characterized much of the plains region of the United States in the 1920s and 1930s.The Central Valley Project was started in the 1930s in response to drought.
1950s
The 1950s drought contributed to the creation of the State Water Project.1976–77
1977 had been the driest year in state history to date. According to the Los Angeles Times, "Drought in the 1970s spurred efforts at urban conservation and the state's Drought Emergency Water Bank came out of drought in the 1980s.".Additionally as drought prediction was essentially random and in response to recent severe drought years, in 1977 the U.S. Department of the Interior, Office of Water Research and Technology contracted Entropy Limited for an exploratory study of the applicability of the entropy minimax method of statistical analysis of multivariate data to the problem of determining the conditional probability of drought one or two years into the future, with the area of special interest being California. Christensen et al. demonstrated an information-theoretic model predicted the probability that precipitation will be below or above average with modest but statistically significant skill one, two and even three years into the future. It was this pioneering work that discovered the influence of El Nino-Southern Oscillation on US weather forecasting.
1986–1992
California endured one of its longest droughts ever, observed from late 1986 through late 1992. Drought worsened in 1988 as much of the United States also suffered from severe drought. In California, the six-year drought ended in late 1992 as a significant El Niño event in the Pacific Ocean most likely caused unusual persistent heavy rains.2007–2009
2007–2009 saw three years of drought conditions, the 12th worst drought period in the state's history, and the first drought for which a statewide proclamation of emergency was issued. The drought of 2007–2009 also saw greatly reduced water diversions from the state water project. The summer of 2007 saw some of the worst wildfires in Southern California history.2011–2017
2011-2017 was the longest drought in California beginning December 2011 and ending March 2017.The period between late 2011 and 2014 was the driest in California history since record-keeping began. In May 2015, a state resident poll conducted by Field Poll found that two out of three respondents agreed that it should be mandated for water agencies to reduce water consumption by 25%.
The 2015 prediction of El Niño to bring rains to California raised hopes of ending the drought. In the spring of 2015, the National Oceanic and Atmospheric Administration named the probability of the presence of El Niño conditions until the end of 2015 at 80%. Historically, El Niño conditions were present during sixteen winters between 1951 and 2015. Six of those had below-average rainfall, five had average rainfall, and five had above-average rainfall. However, as of May 2015, drought conditions had worsened and above average ocean temperatures had not resulted in large storms.
The drought led to Governor Jerry Brown's instituting mandatory 25 percent water restrictions in June 2015.
Many millions of California trees died from the drought – approximately 102 million, including 62 million in 2016 alone. By the end of 2016, 30% of California had emerged from the drought, mainly in the northern half of the state, while 40% of the state remained in the extreme or exceptional drought levels. Heavy rains in January 2017 were expected to have a significant benefit to the state's northern water reserves, despite widespread power outages and erosional damage in the wake of the deluge. Among the casualties of the rain was 1,000 year-old Pioneer Cabin Tree in Calaveras Big Trees State Park, which toppled on January 8, 2017.
The winter of 2016–17 turned out to be the wettest on record in Northern California, surpassing the previous record set in 1982–83. Floodwaters caused severe damage to Oroville Dam in early February, prompting the temporary evacuation of nearly 200,000 people north of Sacramento. In response to the heavy precipitation, which flooded multiple rivers and filled most of the state's major reservoirs, Governor Brown declared an official end to the drought on April 7.