Flash flood

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An urban underpass during normal conditions (upper) and after fifteen minutes of heavy rain (lower) Main and University, Charlottesville, during flash flood (comparison).jpg
An urban underpass during normal conditions (upper) and after fifteen minutes of heavy rain (lower)
Driving through a flash-flooded road Driving through flash flood.jpg
Driving through a flash-flooded road
A flash flood after a thunderstorm in the Gobi, Mongolia GobiFlood.JPG
A flash flood after a thunderstorm in the Gobi, Mongolia

A flash flood is a rapid flooding of low-lying areas: washes, rivers, dry lakes and basins. It may be caused by heavy rain associated with a severe thunderstorm, hurricane, tropical storm, or meltwater from ice or snow flowing over ice sheets or snowfields. Flash floods may occur after the collapse of a natural ice or debris dam, or a human structure such as a man-made dam, as occurred before the Johnstown Flood of 1889. Flash floods are distinguished from regular floods by having a timescale of fewer than six hours between rainfall and the onset of flooding. [1] The water that is temporarily available is often used by plants with rapid germination and short growth cycles and by specially adapted animal life.[ citation needed ][ dubious ]

Flood Overflow of water that submerges land that is not normally submerged

A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health.

River Natural flowing watercourse

A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reaching another body of water. Small rivers can be referred to using names such as stream, creek, brook, rivulet, and rill. There are no official definitions for the generic term river as applied to geographic features, although in some countries or communities a stream is defined by its size. Many names for small rivers are specific to geographic location; examples are "run" in some parts of the United States, "burn" in Scotland and northeast England, and "beck" in northern England. Sometimes a river is defined as being larger than a creek, but not always: the language is vague.

Dry lake A basin or depression that formerly contained a standing surface water body

A dry lake is either a basin or depression that formerly contained a standing surface water body, which disappeared when evaporation processes exceeded recharge. If the floor of a dry lake is covered by deposits of alkaline compounds, it is known as an alkali flat. If covered with salt, it is known as a salt flat.



Flash floods can occur under several types of conditions. Flash flooding occurs when it rains rapidly on saturated soil or dry soil that has poor absorption ability. The runoff collects in gullies and streams and, as they join to form larger volumes, often form a fast flowing front of water and debris.

Flash floods most often occur in normally dry areas that have recently received precipitation, but they may be seen anywhere downstream from the source of the precipitation, even many miles from the source. In areas on or near volcanoes, flash floods have also occurred after eruptions, when glaciers have been melted by the intense heat. Flash floods are known to occur in the highest mountain ranges of the United States and are also common in the arid plains of the Southwestern United States. Flash flooding can also be caused by extensive rainfall released by hurricanes and other tropical storms, as well as the sudden thawing effect of ice dams. [2] [3] Human activities can also cause flash floods to occur. When dams fail, a large quantity of water can be released and destroy everything in its path. [3]

Volcano A rupture in the crust of a planetary-mass object that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface

A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.

Glacier Persistent body of ice that is moving under its own weight

A glacier is a persistent body of dense ice that is constantly moving under its own weight; it forms where the accumulation of snow exceeds its ablation over many years, often centuries. Glaciers slowly deform and flow due to stresses induced by their weight, creating crevasses, seracs, and other distinguishing features. They also abrade rock and debris from their substrate to create landforms such as cirques and moraines. Glaciers form only on land and are distinct from the much thinner sea ice and lake ice that form on the surface of bodies of water.

United States Federal republic in North America

The United States of America (USA), commonly known as the United States or America, is a country comprising 50 states, a federal district, five major self-governing territories, and various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is slightly smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U.S. is the third most populous country. The capital is Washington, D.C., and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico. The State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean. The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The extremely diverse geography, climate, and wildlife of the United States make it one of the world's 17 megadiverse countries.


A flash flood greatly inundates a small ditch, flooding barns and ripping out newly installed drain pipes. Canandaigua flood July 23, 2017 barn flooded 4.jpg
A flash flood greatly inundates a small ditch, flooding barns and ripping out newly installed drain pipes.

The United States National Weather Service gives the advice "Turn Around, Don't Drown" for flash floods; that is, it recommends that people get out of the area of a flash flood, rather than trying to cross it. Many people tend to underestimate the dangers of flash floods. What makes flash floods most dangerous is their sudden nature and fast-moving water. A vehicle provides little to no protection against being swept away; it may make people overconfident and less likely to avoid the flash flood. More than half of the fatalities attributed to flash floods are people swept away in vehicles when trying to cross flooded intersections. [4] As little as 2 feet (0.61 m) of water is enough to carry away most SUV-sized vehicles. [5] The U.S. National Weather Service reported in 2005 that, using a national 30-year average, more people die yearly in floods, 127 on average, than by lightning (73), tornadoes (65), or hurricanes (16). [6]

National Weather Service United States weather agency

The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the purposes of protection, safety, and general information. It is a part of the National Oceanic and Atmospheric Administration (NOAA) branch of the Department of Commerce, and is headquartered in Silver Spring, Maryland, within the Washington metropolitan area. The agency was known as the United States Weather Bureau from 1890 until it adopted its current name in 1970.

Lightning Atmospheric discharge of electricity

Lightning is a violent and sudden electrostatic discharge where two electrically charged regions in the atmosphere temporarily equalize themselves, usually during a thunderstorm.

Tornado Violently rotating column of air that is in contact with both the earths surface and a cumulonimbus cloud in the air

A tornado is a rapidly rotating column of air that is in contact with both the surface of the Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. The windstorm is often referred to as a twister, whirlwind or cyclone, although the word cyclone is used in meteorology to name a weather system with a low-pressure area in the center around which, from an observer looking down toward the surface of the earth, winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern. Tornadoes come in many shapes and sizes, and they are often visible in the form of a condensation funnel originating from the base of a cumulonimbus cloud, with a cloud of rotating debris and dust beneath it. Most tornadoes have wind speeds less than 110 miles per hour (180 km/h), are about 250 feet (80 m) across, and travel a few miles before dissipating. The most extreme tornadoes can attain wind speeds of more than 300 miles per hour (480 km/h), are more than two miles (3 km) in diameter, and stay on the ground for dozens of miles.

In deserts, flash floods can be particularly deadly for several reasons. First, storms in arid regions are infrequent, but they can deliver an enormous amount of water in a very short time. Second, these rains often fall on poorly absorbent and often clay-like soil, which greatly increases the amount of runoff that rivers and other water channels have to handle. These regions tend not to have the infrastructure that wetter regions have to divert water from structures and roads, such as storm drains, culverts, and retention basins, either because of sparse population or poverty, or because residents believe the risk of flash floods is not high enough to justify the expense. In fact, in some areas, desert roads frequently cross a dry river and creek beds without bridges. From the driver's perspective, there may be clear weather, when a river unexpectedly forms ahead of or around the vehicle in a matter of seconds. [7] Finally, the lack of regular rain to clear water channels may cause flash floods in deserts to be headed by large amounts of debris, such as rocks, branches, and logs.

Desert Area of land where little precipitation occurs

A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one-third of the land surface of the world is arid or semi-arid. This includes much of the polar regions where little precipitation occurs and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.

Surface runoff The flow of excess stormwater, meltwater, or water from other sources over the Earths surface

Surface runoff is the flow of water that occurs when excess storm water, melt water, or other sources flows over the Earth's surface. This might occur because soil is saturated to full capacity, because rain arrives more quickly than soil can absorb it, or because impervious areas send their runoff to surrounding soil that cannot absorb all of it. Surface runoff is a major component of the water cycle. It is the primary agent in soil erosion by water.

Retention basin Detention basin

A retention basin, sometimes called a wet pond,wet detention basin or stormwater management pond, is an artificial lake with vegetation around the perimeter, and includes a permanent pool of water in its design. It is used to manage stormwater runoff to prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay.

Deep slot canyons can be especially dangerous to hikers as they may be flooded by a storm that occurs on a mesa miles away. The flood sweeps through the canyon; the canyon makes it difficult to climb up and out of the way to avoid the flood.

Slot canyon

A slot canyon is a narrow canyon, formed by the wear of water rushing through rock. A slot canyon is significantly deeper than it is wide. Some slot canyons can measure less than 1 metre (3 ft) across at the top but drop more than 30 metres (100 ft) to the floor of the canyon.

Mesa Elevated area of land with a flat top and sides that are usually steep cliffs

Mesa is the American English term for tableland, an elevated area of land with a flat top and sides that are usually steep cliffs. It takes its name from its characteristic table-top shape. It may also be called a table hill, table-topped hill or table mountain. It is larger than a butte, which it otherwise resembles closely.

Significant examples

Johnstown Flood Massive flood of Johnstown, Pennsylvania caused by the collapse of the South Fork Dam

The Johnstown Flood occurred on May 31, 1889, after the catastrophic failure of the South Fork Dam on the Little Conemaugh River 14 miles (23 km) upstream of the town of Johnstown, Pennsylvania. The dam broke after several days of extremely heavy rainfall, releasing 14.55 million cubic meters of water. With a volumetric flow rate that temporarily equaled the average flow rate of the Mississippi River, the flood killed more than 2,200 people and accounted for $17 million of damage.

Oregon State of the United States of America

Oregon is a state in the Pacific Northwest region on the West Coast of the United States. The Columbia River delineates much of Oregon's northern boundary with Washington, while the Snake River delineates much of its eastern boundary with Idaho. The parallel 42° north delineates the southern boundary with California and Nevada. Oregon is one of only three states of the contiguous United States to have a coastline on the Pacific Ocean.

A flash flood on the Waiau Stream at Kopuawhara in New Zealand on 19 February 1938 destroyed a railway construction workers camp killing 20 men and one woman, Martha Quinn.

See also

Related Research Articles

Cloudburst short and very intense rain

A cloudburst is an extreme amount of precipitation in a short period of time, sometimes accompanied by hail and thunder, which is capable of creating flood conditions. A cloudburst can suddenly dump large amounts of water e.g. 25 mm of precipitation corresponds to 25,000 metric tons/km2. However, cloudbursts are infrequent as they occur only via orographic lift or occasionally when a warm air parcel mixes with cooler air, resulting in sudden condensation. At times, a large amount of runoff from higher elevations is mistakenly conflated with a cloudburst. The term "cloudburst" arose from the notion that clouds were akin to water balloons and could burst, resulting in rapid precipitation. Though this idea has since been disproven, the term remains in use.

Hurricane Diane Category 2 Atlantic hurricane in 1955

Hurricane Diane was the costliest Atlantic hurricane of its time, causing $813.7 million in damage. The inclusion of loss of business and personal revenue increased the total to over $1 billion. One of three hurricanes to hit North Carolina during the 1955 Atlantic hurricane season, it formed on August 7 from a tropical wave between the Lesser Antilles and Cape Verde. Diane initially moved west-northwestward with little change in its intensity, but began to strengthen rapidly after turning to the north-northeast. On August 12, the hurricane reached peak sustained winds of 105 mph (165 km/h), making it a Category 2 hurricane. Gradually weakening after veering back west, Diane made landfall near Wilmington, North Carolina, as a strong tropical storm on August 17, just five days after Hurricane Connie struck near the same area. Diane weakened further after moving inland, at which point the United States Weather Bureau noted a decreased threat of further destruction. The storm turned to the northeast, and warm waters from the Atlantic Ocean helped produce record rainfall across the northeastern United States. On August 19, Diane emerged into the Atlantic Ocean southeast of New York City, becoming extratropical two days later and completely dissipating by August 23.

San Gabriel River (California) river in Los Angeles County, California, United States

The San Gabriel River is a mostly urban waterway flowing 58 miles (93 km) southward through Los Angeles and Orange Counties, California in the United States. It is the central of three major rivers draining the Greater Los Angeles Area, the others being the Los Angeles River and Santa Ana River. The river's watershed stretches from the rugged San Gabriel Mountains to the heavily developed San Gabriel Valley and a significant part of the Los Angeles coastal plain, emptying into the Pacific Ocean between the cities of Long Beach and Seal Beach.

Arroyo (creek) A dry creek or stream bed with flow after rain

An arroyo, also called a wash, is a dry creek, stream bed or gulch that temporarily or seasonally fills and flows after sufficient rain. Flash floods are common in arroyos following thunderstorms.

This article describes severe weather terminology used by the National Weather Service (NWS) in the United States. The NWS, a government agency operating as an arm of the National Oceanic and Atmospheric Administration (NOAA) branch of the United States Department of Commerce (DoC), defines precise meanings for nearly all of its weather terms. This article describes NWS terminology and related weather scales used by the agency. Some terms may be specific to certain cities or regions.

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, 1901 through 2000, inclusive.

Natural disasters in India

Natural disasters in India, many of them related to the climate of India, cause massive losses of life and property. Droughts, flash floods, cyclones, avalanches, landslides brought by torrential rains, and snowstorms pose the greatest threats. A natural disaster might be caused by earthquakes, flooding, volcanic eruption, landslides, hurricanes etc. In order to be classified as a disaster it will have profound environmental effect and/or human loss and frequently incurs financial loss. Other dangers include frequent summer dust storms, which usually track from north to south; they cause extensive property damage in North India and deposit large amounts of dust from arid regions. Hail is also common in parts of India, causing severe damage to standing crops such as rice and wheat and many more crops.

Floods in the United States: 2001–present

Floods in the United States: 2001–present is a list of flood events which were of significant impact to the country since 2001, inclusive. Floods are generally caused by excessive rainfall, excessive snowmelt, storm surge from hurricanes, and dam failure.

Severe weather

Severe weather refers to any dangerous meteorological phenomena with the potential to cause damage, serious social disruption, or loss of human life. Types of severe weather phenomena vary, depending on the latitude, altitude, topography, and atmospheric conditions. High winds, hail, excessive precipitation, and wildfires are forms and effects of severe weather, as are thunderstorms, downbursts, tornadoes, waterspouts, tropical cyclones, and extratropical cyclones. Regional and seasonal severe weather phenomena include blizzards (snowstorms), ice storms, and duststorms.

Typhoon Parma Pacific typhoon in 2009

Typhoon Parma, known in the Philippines as Typhoon Pepeng, was the second typhoon to affect the Philippines within the span of a week during September 2009.

Tropical Storm Domoina South-West Indian tropical storm in 1984

Severe Tropical Storm Domoina in 1984 caused 100 year floods in South Africa and record rainfall in Swaziland. The fourth named storm of the season, Domoina developed on January 16 off the northeast coast of Madagascar. With a ridge to the north, the storm tracked generally westward and later southwestward. On January 21, Domoina struck eastern Madagascar, the third storm in six weeks to affect the nation; collectively, the storms caused 42 deaths and $25 million in damage (1984 USD). After crossing the country, Domoina strengthened in the Mozambique Channel to peak 10 minute sustained winds of 95 km/h (60 mph). On January 28, the storm made landfall in southern Mozambique, and slowly weakened over land. Domoina crossed into Swaziland and later eastern South Africa before dissipating on February 2.

Heppner flood of 1903

The Heppner flood of 1903 was a major flash flood along Willow Creek responsible for destroying a large portion of Heppner, Oregon, United States, on June 14, 1903. With a death toll of 324 people, it remains the deadliest natural disaster in Oregon, and the second deadliest flash flood in the entire United States, behind the 1889 Johnstown Flood and ahead of the 1972 Black Hills Flood. The flood caused over $600,000 in damage, equivalent to $16.7 million today.

2011 Souris River flood

The 2011 Souris/Mouse River flood in Canada and the United States occurred in June and was greater than a hundred-year flooding event for the river. The US Army Corps of Engineers estimated the flood to have a recurrence interval of two to five centuries.

Flooding occurs when an extreme volume of water is carried by rivers, creeks and many other geographical features into areas where the water cannot be drained adequately. Often during times of heavy rainfall, drainage systems in residential areas are not adequate, or unchecked civil development severely impedes the functionality of an otherwise acceptable drainage system. Floods cause extremely large numbers of fatalities in every country, but due to India's extremely high population density and often under-enforced development standards, a large amount of damages and many deaths which could be otherwise avoided, are allowed to happen. India witnesses flood due to excessive rain which then results in overflow of rivers, lakes and dams, which adds to cause large amounts of damage to people's lives and property. In the past, India has witnessed many of the largest, most catastrophic floods, causing irreparable damage to people's livelihood, property, and crucial infrastructure.

Hurricane Linda (2015)

Hurricane Linda was a strong tropical cyclone in September 2015 that resulted in heavy rains across portions of Mexico and the Southwestern United States. The seventeenth named storm and eleventh hurricane of the season, Linda developed southwest of Mexico from a low pressure area on September 5. Under warm sea surface temperatures and low to moderate wind shear, the system intensified into Tropical Storm Linda by September 6 and a hurricane by the next day. A well-defined eye soon formed within the storm's central dense overcast and Linda reached its peak intensity as a 125 mph (205 km/h) Category 3 major hurricane on the Saffir–Simpson hurricane wind scale on September 8. Thereafter, the storm moved into a stable environment and an area of lower sea surface temperatures, causing rapid weakening. Convective activity dissipated and Linda degenerated into a remnant low on September 10. The lingering system persisted southwest of Baja California, ultimately opening up into a trough on September 14.

2017 California floods

The 2017 California floods were a series of floods that affected parts of California in the first half of 2017. Northern California saw its wettest winter in almost a century, breaking the previous record set in the winter of 1982–83. Flooding related to the same storm systems also impacted parts of western Nevada and southern Oregon. Damage to California roads and highways alone was estimated at over $1.05 billion.

2018 Hawaii floods

In April 2018, a series of thunderstorms produced record-breaking rainfall on the Hawaiian Islands of Kauaʻi and Oahu. An upper-level low moved across the area on April 13, generating a mesoscale convective system that moved over eastern Oahu, producing localized heavy rainfall that reached 5.55 in (141 mm). The heaviest rainfall occurred on northern Kauaʻi. There, a rain gauge owned by the Waipā Foundation, just west of Hanalei, recorded 49.69 in (1,262 mm) of rainfall in the 24 hours between 12:45 p.m. on April 14 and 15. This was the greatest 24-hour rainfall total on record in the United States, surpassing the previous record of 43 in (1,100 mm) in Alvin, Texas on July 25–26, 1979, set during Tropical Storm Claudette. Through the entire event, the same gauge recorded a total of 54.37 in (1,381 mm) of rain.


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Further reading