All types of floods can occur in California, though 90 percent of them are caused by river flooding in lowland areas. [1] [2] Such flooding generally occurs as a result of excessive rainfall, excessive snowmelt, excessive runoff, levee failure, tsunami, poor planning or built infrastructure, or a combination of these factors. Below is a list of flood events that were of significant impact to California.
A 2022 study found that Climate change in California will increase the extremity of water cycle events such as droughts and megafloods, greatly increasing the severity of future floods due to atmospheric rivers. [2] In part this is due to the expectation that the Sierra Nevada mountains, which typically retain water as snow, will no longer be as cold, reducing snowpack in favor or more runoff. [2] Thus water reserves do not accumulate, leading to drought conditions, even if there is more precipitation. [3]
Every county in California has experienced a flood, which is mostly likely to be caused by an atmospheric river, which is a narrow corridor of moisture in the air that travels a long distance to produce heavy rainfall. [4] The state of California spends more than US$2.8 billion annually on maintaining or building flood control projects. [5]
Geologic evidence indicates that "megafloods" occurred in the California region in the following years A.D.: 212, 440, 603, 1029, c. 1300, 1418, 1605, and 1750. [6] [7] Prior to European settlement, these early floods predominantly affected the indigenous peoples of California.
The Central Valley is a broad, elongated, flat valley that dominates the interior of California. It is 40–60 mi (60–100 km) wide and runs approximately 450 mi (720 km) from north-northwest to south-southeast, inland from and parallel to the Pacific coast of the state. It covers approximately 18,000 sq mi (47,000 km2), about 11% of California's land area. The valley is bounded by the Coast Ranges to the west and the Sierra Nevada to the east.
Pineapple Express is a specific recurring atmospheric river both in the waters immediately northeast of the Hawaiian Islands and extending northeast to any location along the Pacific coast of North America. It is a non-technical term and a meteorological phenomenon. It is characterized by a strong and persistent large-scale flow of warm moist air, and the associated heavy precipitation. A Pineapple Express is an example of an atmospheric river, which is a more general term for such relatively narrow corridors of enhanced water vapor transport at mid-latitudes around the world.
Lake Oroville is a reservoir formed by the Oroville Dam impounding the Feather River, located in Butte County, northern California. The lake is situated 5 miles (8 km) northeast of the city of Oroville, within the Lake Oroville State Recreation Area, in the western foothills of the Sierra Nevada. Known as the second-largest reservoir in California, Lake Oroville is treated as a keystone facility within the California State Water Project by storing water, providing flood control, recreation, freshwater releases to assist in controlling the salinity intrusion into the Sacramento-San Joaquin Delta and protecting fish and wildlife.
Hurricane Kathleen was a Category 1 Pacific hurricane that had a destructive impact in California. On September 7, 1976, a tropical depression formed; two days later it accelerated north towards the Baja California Peninsula. Kathleen brushed the Pacific coast of the peninsula as a hurricane on September 9 and made landfall as a fast-moving tropical storm the next day. With its circulation intact and still a tropical storm, Kathleen headed north into the United States and affected California and Arizona. Kathleen finally dissipated late on September 11.
The Los Angeles flood of 1938 was one of the largest floods in the history of Los Angeles, Orange, and Riverside Counties in southern California. The flood was caused by two Pacific storms that swept across the Los Angeles Basin in February-March 1938 and generated almost one year's worth of precipitation in just a few days. Between 113–115 people were killed by the flooding. The Los Angeles, San Gabriel, and Santa Ana Rivers burst their banks, inundating much of the coastal plain, the San Fernando and San Gabriel Valleys, and the Inland Empire. Flood control structures spared parts of Los Angeles County from destruction, while Orange and Riverside Counties experienced more damage.
Floods in the United States are generally caused by excessive rainfall, excessive snowmelt, and dam failure. Below is a list of flood events that were of significant impact to the country during the 20th century, from 1900 through 1999, inclusive.
Floods in the United States (2000–present) is a list of flood events which were of significant impact to the country during the 21st century, since 2000. Floods are generally caused by excessive rainfall, excessive snowmelt, storm surge from hurricanes, and dam failure.
The climate of Los Angeles is mild to hot year-round, and mostly dry. It is classified as borderline Mediterranean and semi-arid. The city is characterized by seasonal changes in rainfall—with a dry summer and a winter rainy season. Under the Köppen climate classification, the coastal areas are classified as BSh and Csb, while the inland areas are classified as BSh and Csa.
The Great Flood of 1862 was the largest flood in the recorded history of California, Oregon, and Nevada, inundating the western United States and portions of British Columbia and Mexico. It was preceded by weeks of continuous rains and snows that began in Oregon in November 1861 and continued into January 1862. This was followed by a record amount of rain from January 9–12, and contributed to a flood that extended from the Columbia River southward in western Oregon, and through California to San Diego, as well as extending as far inland as the Washington Territory, the Utah Territory, and the western New Mexico Territory.
An atmospheric river (AR) is a narrow corridor or filament of concentrated moisture in the atmosphere. Other names for this phenomenon are tropical plume, tropical connection, moisture plume, water vapor surge, and cloud band.
The Christmas flood of 1964 was a major flood in the United States' Pacific Northwest and some of Northern California between December 18, 1964, and January 7, 1965, spanning the Christmas holiday.
The ARkStorm is a hypothetical megastorm, whose proposal is based on repeated historical occurrences of atmospheric rivers and other major rain events first developed and published by the Multi-Hazards Demonstration Project (MHDP) of the United States Geological Survey (USGS) in 2010. An updated model was published as ARkStorm 2.0 in 2022.
The Los Angeles County flood of 2005 was the first large flood in Los Angeles County since 1938. It affected communities near the Los Angeles River and areas ranging from Santa Barbara County in the north to Orange and San Diego Counties in the south, as well as Riverside and San Bernardino Counties to the east. Large amounts of rain in January caused the Los Angeles River basin to overflow. The Ventura, Santa Ynez, and Santa Clara Rivers also flooded.
The January 2010 North American winter storms were a group of seven powerful winter storms that affected Canada and the Contiguous United States, particularly California. The storms developed from the combination of a strong El Niño episode, a powerful jet stream, and an atmospheric river that opened from the West Pacific Ocean into the Western Seaboard. The storms shattered multiple records across the Western United States, with the sixth storm breaking records for the lowest recorded air pressure in multiple parts of California, which was also the most powerful winter storm to strike the Southwestern United States in 140 years. The fourth, fifth, and sixth storms spawned several tornadoes across California, with at least 6 tornadoes confirmed in California ; the storms also spawned multiple waterspouts off the coast of California. The storms dumped record amounts of rain and snow in the Western United States, and also brought hurricane-force winds to the U.S. West Coast, causing flooding and wind damage, as well as triggering blackouts across California that cut the power to more than 1.3 million customers. The storms killed at least 10 people, and caused more than $66.879 million in damages.
The December 2014 North American storm complex was a powerful winter storm that impacted the West Coast of the United States, beginning on the night of December 10, 2014, resulting in snow, wind, and flood watches. Fueled by the Pineapple Express, an atmospheric river originating in the tropical waters of the Pacific Ocean adjacent to the Hawaiian Islands, the storm was the strongest to affect California since January 2010. The system was also the single most intense storm to impact the West Coast, in terms of minimum low pressure, since a powerful winter storm in January 2008. The National Weather Service classified the storm as a significant threat, and issued 15 warnings and advisories, including a Blizzard Warning for the Northern Sierra Nevada.
The historical and ongoing droughts in California result from various complex meteorological phenomena, some of which are not fully understood by scientists.
Flooding in 2017 affected parts of California in the first half of the year. Northern California saw its wettest winter in almost a century, breaking the record set in 1982–83. The same storm systems also flooded parts of western Nevada and southern Oregon. The damage was estimated at $1.55 billion ($1,926,663,046 today), including damage to California roads and highways estimated at more than $1.05 billion.
In February 2017, heavy rainfall damaged Oroville Dam's main and emergency spillways, prompting the evacuation of more than 180,000 people living downstream along the Feather River and the relocation of a fish hatchery.
Periods of heavy rainfall caused by multiple atmospheric rivers in California between December 31, 2022, and March 25, 2023, resulted in floods that affected parts of Southern California, the California Central Coast, Northern California and Nevada. The flooding resulted in property damage and at least 22 fatalities. At least 200,000 homes and businesses lost power during the December-January storms and 6,000 individuals were ordered to evacuate.
Although the media and some officials were quick to link a series of powerful storms to climate change, researchers interviewed by The Times said they had yet to see evidence of that connection. Instead, the unexpected onslaught of rain and snow after three years of punishing drought appears akin to other major storms that have struck California every decade or more since experts began keeping records in the 1800s.
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