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A flash flood after a thunderstorm in the Gobi, Mongolia A flash flood is a rapid
flood Flash flooding caused by heavy rain falling in a short amount of time. 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. F ...
ing of low-lying areas: washes,
river 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. Sm ...
s,
dry lake A dry lake, also known as a playa, 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 alkali ...
s and depressions. It may be caused by heavy
rain Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fres ...
associated with a
severe thunderstorm A thunderstorm, (also known as an electrical storm or a lightning storm) is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. (There are relativitly weak thunderstorms,some ...
,
hurricane A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and/or squalls. Dependin ...

hurricane
,
tropical storm A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and/or squalls. Dependin ...
, or
meltwater Meltwater is water released by the melting of snow or ice, including glacial ice, tabular icebergs and ice shelves over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing. Meltwater can be p ...
from ice or snow flowing over ice sheets or snowfields. Flash floods may also occur after the collapse of a natural
ice Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color. In the Solar System, ice is abundant and occur ...
or
debris dam A landslide dam or barrier lake is a natural damming of a river by some kind of landslides, such as debris flows and rock avalanches, or by volcanic eruptions. If the damming landslides are caused by an earthquake, it may also be called a quake lake ...
, or a human structure such as a man-made
dam A dam is a barrier that stops or restricts the flow of water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aquacultur ...
, as occurred before the
Johnstown Flood The Johnstown Flood (locally, the Great Flood of 1889) occurred on Friday, May 31, 1889, after the catastrophic failure of the South Fork Dam, located on the south fork of the Little Conemaugh River, upstream of the town of Johnstown, Pennsylvan ...
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. The water that is temporarily available is sometimes used by certain plants for growth. However, plants that thrive in drier areas can be harmed by flooding, as the plants can become stressed by the large amount of water.


Causes

Flash floods most often occur in 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
volcano 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. On Earth, volcanoes are most often found where tectonic plates are d ...
es, flash floods have also occurred after eruptions, when
glacier A glacier ( or ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. Glaciers slowly deform and flow under stres ...
s have been melted by the intense heat. Flash floods are known to occur in the highest mountain ranges of the
United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major self-governing territories, 326 India ...
and are also common in the arid plains of the Southwestern United States. Flash flooding can also be caused by extensive rainfall released by
hurricane A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and/or squalls. Dependin ...
s and other
tropical storm A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and/or squalls. Dependin ...
s, as well as the sudden thawing effect of ice dams. 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.


Hazards

The United States
National Weather Service 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 purp ...
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. As little as of water is enough to carry away most SUV-sized vehicles. 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 Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions in the atmosphere or ground temporarily equalize themselves, causing the instantaneous release of as much as one gigajoule of energy. ...
(73),
tornado A tornado is a violently 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 cyclon ...
es (65), or
hurricane A tropical cyclone is a rapidly rotating storm system characterized by a low-pressure center, a closed low-level atmospheric circulation, strong winds, and a spiral arrangement of thunderstorms that produce heavy rain and/or squalls. Dependin ...

hurricane
s (16). In
desert upright=1.5, alt=see caption, Sand dunes in the Rub' al Khali ("Empty quarter") in the United Arab Emirates A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for ...
s, 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 Runoff, run-off or RUNOFF may refer to: * RUNOFF, the first computer text-formatting program * Runoff or run-off, another name for bleed, printing that lies beyond the edges to which a printed sheet is trimmed * Runoff or run-off, a stock market te ...
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 basin Trounce Pond, a retention basin landscaped with natural grassland plants, in Saskatoon, Saskatchewan, Canada">Saskatchewan.html" style="text-decoration: none;"class="mw-redirect" title="Saskatoon, Saskatchewan">Saskatoon, Saskatchewan, Can ...
s, 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. 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. Deep
slot canyon A slot canyon is a long, narrow, deep and tortuous channel or drainageway with sheer rock walls that are typically eroded into either sandstone or other sedimentary rock. A slot canyon has depth-to-width ratios that typically exceed 10:1 over most ...
s can be especially dangerous to hikers as they may be flooded by a storm that occurs on a
mesa A mesa is an isolated, flat-topped elevation, ridge or hill, which is bounded from all sides by steep escarpments and stands distinctly above a surrounding plain. Mesas characteristically consist of flat-lying soft sedimentary rocks capped by a ...
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.


Flash flood impacts

Flash floods induce severe impacts in both the built and the natural environment. Especially within urban areas, the effects of flash floods can be catastrophic and show extensive diversity, ranging from damages in buildings and infrastructure to impacts on vegetation, human lives and livestock. An impact severity scale is proposed in 2020 providing a coherent overview of the flash flood effects through the classification of impact types and severity and mapping their spatial extent in a continuous way across the floodplain. Depending on the affected elements, the flood effects are grouped into 4 categories: (i) impacts on built environment (ii) impacts on man-made mobile objects,(iii) impacts on the natural environment (including vegetation, agriculture, geomorphology, and pollution) and (iv) impacts on the human population (entrapments, injuries, fatalities). The scale was proposed as a tool on prevention planning, as the resulting maps offer insights on future impacts, highlighting the high severity areas.


Significant examples

* 1889:
Johnstown Flood The Johnstown Flood (locally, the Great Flood of 1889) occurred on Friday, May 31, 1889, after the catastrophic failure of the South Fork Dam, located on the south fork of the Little Conemaugh River, upstream of the town of Johnstown, Pennsylvan ...
, Pennsylvania, U.S.: more than 2,200 people dead * 1903: Heppner Flood of 1903;
Oregon Oregon () is a state in the Pacific Northwest region of the Western 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. Th ...
,
United States The United States of America (USA), commonly known as the United States (U.S. or US), or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major self-governing territories, 326 India ...
: 247 dead, 25% of the city * 1938:
Los Angeles Flood of 1938#REDIRECT Los Angeles flood of 1938 {{R from other capitalisation ...
, California, U.S.: 115 dead * 1938: Kopuawhara flash flood of 1938, Mahia Peninsula, New Zealand: 21 dead * 1952: Lynmouth disaster, England: 34 dead * 1963: Petra Flash Flood, Jordan: 23 dead * 1963: Vajont dam disaster, Italy: 1910 dead * 1967: Flash flood in Lisbon, Portugal: 464 dead * 1969: Nelson County, Virginia, US: 123 dead * 1971: Kuala Lumpur floods, Malaysia: 32 dead * 1972: The Black Hills flood, South Dakota, U.S.: 238 dead * 1976: The Big Thompson River flood, Colorado, U.S.: 143 dead * 1997:
Antelope Canyon Antelope Canyon is a slot canyon in the American Southwest, on Navajo land east of Page, Arizona. It includes two separate, scenic slot canyon sections, referred to as Upper Antelope Canyon (or The Crack), and Lower Antelope Canyon (or The Corkscre ...
, a popular tourist attraction north of Page, Arizona:11 dead * 2003:
Bukit Lawang One of orangutans is being taken care at Bukit Lawang. Bukit Lawang is a small tourist village on the bank of Bahorok River in North Sumatra province of Indonesia. Situated approximately 86 km northwest of the city of Medan, Bukit Lawang is ...
in
Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of more than seventeen thousand islands, including Sumatra, ...

Indonesia
239 people (5 of them were tourists) were killed * 2006: Surat flood * 2006:
Jember Regency Jember Regency is a regency of East Java province, Indonesia. The population was 2,332,726 at the 2010 census; the latest official estimate (as at 2015) is 2,406,142. Its administrative capital is the urban area of Jember, which with 332,611 inha ...
in Indonesia 59 people dead * 2007: Sudan floods, 64 dead. * 2009: September 26 in Metro Manila primarily Marikina, Taguig City, and Pasig City; and many municipalities of the provinces of Rizal, Bulacan and Laguna leaving more than 100 dead and thousands homeless. It also submerged several municipalities under feet of deep water for several weeks. * 2009: October 1, Giampilieri, Messina, 37 dead. See also 2009 Messina floods and mudslides. * 2010: Madeira archipelago, 2010 Madeira floods and mudslides, 42 dead * 2011: 2010-2011 Queensland Floods, Lockyer Valley, Queensland, Australia. 21 dead, mainly in the town of Grantham, Queensland, Grantham. * 2011: Philippines, Cagayan de Oro and Iligan City, 17 December 2011. At least 1200 dead * 2012: May 5, Nearly three weeks of damming left 72 dead in the Seti Gorge in Upper Seti Basin. Rock and avalanche fall from the western part of Annapurna IV mountain in Pokhara, Nepal. * 2012: Krasnodarskiy Kray, Russia. 2012 Russian floods, 172 dead following a flash flood that struck at 2 A.M. local time on 7 July. Main cities that were hit are Krymsk and Gelendzhik. * 2013: Uttarakhand, Uttarakhand, India: 822 dead *2013: November 17–19, Northeast Sardinia: 18 dead, 3000 homeless. See also 2013 Sardinia floods *2013: Port Louis, Mauritius: 11 dead *2013 Argentina floods, 2013: Argentina floods: 99+ dead *2013: Kedarnath, Uttarakhand, India: ~5000 dead *2014: Srinagar, Jammu & Kashmir, India: approximately 300 dead. *2014: Serbia, Bosnia and Croatia: 30+ dead *2015: May 25, Central Texas floods: 25+ dead *2016: June 25, West Virginia floods: 24+ dead *2016 Maryland flood, 2016: July 30, Ellicott City, Maryland: 2 dead *2016 Louisiana floods, 2016: August 13, South Louisiana floods: 13 dead. *2016: September 20, Garut Regency in Indonesia floods: 33 dead *2017: November 15, Νότια Αττική (West Attiki), Greece floods: 23 dead *2018: April 26, Tzafit Canyon, Israel flood: 10 dead *2018 Maryland flood, 2018: May 27, Ellicott City, Maryland: Flood was considered worse than the one that occurred just under 2016 Maryland flood, two years prior: 1 dead *2018: August 20, Raganello Canyon, Italy flood: 10 dead *2018: September 12, parts of Spain, Italy, France flood: 15 dead *2018: October 15–16, Aude region, France flood, 15 dead and 99 injured *2018: October 25, Dead sea flash flood: 21 dead *2019: Flash Flood in Southern Iran: at least 23 dead; also in Northern Afghanistan: at least 16 dead


See also

* Storm surge * Coastal flood * Drowning * Cloudburst * Flash flood watch * Flash flood warning * Flash Flood Guidance Systems * Freshet * Huayco * Lifesaving


References


Further reading

*


External links

* Public clip of the Fochabers flood in Moray September 9
Decision tree to choose an uncertainty method for hydrological and hydraulic modelling
choosing an uncertainty analysis for flood modelling.
Great footage of flash floods
in the arid midwest heading down dry washes after heavy rain.

of central Texas flash flood alley.
Workshop Proceedings Flash Flood Management

Workshop Proceedings Flash Flood Forecasting

Hydrologic Research Center
{{DEFAULTSORT:Flash flood Flood Hydrology