Flash flood

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An urban underpass during normal conditions (upper) and after fifteen minutes of heavy rain (lower)
Driving through a flash-flooded road
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 depressions. 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 also 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]

Flash floods are a significant hazard, causing more fatalities in the U.S. in an average year than lightning, tornadoes, or hurricanes. Flash floods can also deposit large quantities of sediments on floodplains and can be destructive of vegetation cover not adapted to frequent flood conditions.

Causes[]

Flash flooded road in Northern Mexico, after a 3-5 hour long thunderstorm that occurred during a drought that lasted nearly 1 year

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 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]

Hazards[]

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]

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.[7] 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.[8] 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.[9]

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. For example, a cloudburst in southern Utah on 14 September 2015 resulted in 20 flash flood fatalities, of which seven fatalities occurred at Zion National Park when hikers were trapped by floodwaters in a slot canyon.[10]

Flash flood impacts[]

Flash floods induce severe impacts in both the built and the natural environment. 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. The effects are particularly difficult to characterize in urban areas.[11]

Researchers have used datasets such as the Severe Hazards Analysis and Verification Experiment (SHAVE) and the U.S. National Weather Service (NWS) Storm Data datasets to connect the impact of flash floods with the physical processes involved in flash flooding. This should increase the reliability of flash flood impact forecasting models.[12] Analysis of flash floods in the United States between 2006 and 2012 shows that injuries and fatalities are most likely in small, rural catchments, that the shortest events are also the most dangerous, that the hazards are greatest after nightfall, and that a very high fraction of injuries and fatalities involve vehicles.[13]

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.[11]

Flash floods can cause rapid soil erosion.[14] Much of the Nile delta sedimentation may come from flash flooding in the desert areas that drain into the Nile River.[15] However, flash floods of short duration produce relatively little bedrock erosion or channel widening, having their greatest impact from sedimentation on the floodplain.[16]

Some wetlands plants, such as certain varieties of rice, are adapted to endure flash flooding.[17] However, plants that thrive in drier areas can be harmed by flooding, as the plants can become stressed by the large amount of water.[18][19]

Significant examples[]

Main article: List of flash floods
  • 1889: Johnstown Flood, Pennsylvania, U.S.: more than 2,200 people dead
  • 1903: Heppner Flood of 1903; Oregon, United States: 247 dead, 25% of the city
  • 1938: Los Angeles Flood of 1938, 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
  • 1991: The Ormoc City tragedy, Ormoc, Philippines: ≈8,000 dead
  • 1997: Antelope Canyon, a popular tourist attraction north of Page, Arizona:11 dead
  • 2003: Bukit Lawang in Indonesia 239 people (5 of them were tourists) were killed
  • 2006:
  • 2006: Jember Regency in Indonesia 59 people dead
  • 2007: Sudan floods, 64 dead.
  • 2009: September 26 in Metro Manila primarily Marikina, Taguig, and Pasig; and several municipalities in 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 floods and mudslides, 51 dead
  • 2011: Lockyer Valley, Queensland, Australia. 21 dead, mainly in the town of 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.[20]
  • 2012: Krasnodarskiy Kray, Russia. 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.[21][22]
  • 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: 99+ dead
  • 2013: Kedarnath, Uttarakhand, India: ≈5000 dead[23]
  • 2014: Srinagar, Jammu & Kashmir, India: approximately 300 dead.[citation needed]
  • 2014: Serbia, Bosnia and Croatia: 30+ dead
  • 2015: May 25, Central Texas floods: 25+ dead
  • 2016: June 25, West Virginia floods: 24+ dead
  • 2016: July 30, Ellicott City, Maryland: 2 dead[24]
  • 2016: August 13, South Louisiana floods: 13 dead.[25]
  • 2016: September 20, Garut Regency in Indonesia floods: 33 dead
  • 2017: July 15, Gila County, Arizona: 10 dead
  • 2017: November 15, Νότια Αττική (West Attiki), Greece floods: 23 dead
  • 2018: April 26, Tzafit Canyon, Israel flood: 10 dead[26]
  • 2018: May 27, Ellicott City, Maryland: Flood was considered worse than the one that occurred just under two years prior: 1 dead [27]
  • 2018: August 20, Raganello Canyon, Italy flood: 10 dead[28]
  • 2018: September 12, parts of Spain, Italy, France flood: 15 dead[29]
  • 2018: October 15–16, Aude region, France flood, 15 dead and 99 injured[30]
  • 2018: October 25, Dead sea flash flood: 21 dead[31]
  • 2019: Flash Flood in Southern Iran: at least 23 dead;[32] also in Northern Afghanistan: at least 16 dead[33]

See also[]

References[]

  1. ^ "Flash Flooding Definition". National Weather Service. Retrieved August 31, 2017.
  2. ^ WeatherEye (2007). "Flash Flood!". Sinclair Acquisition IV, Inc. Archived from the original on 2009-02-27. Retrieved 2009-09-09.
  3. ^ Jump up to: a b National Weather Service Forecast Office Morristown, Tennessee (2006-03-07). "Definitions of flood and flash flood". National Weather Service Southern Region Headquarters. Retrieved 2009-09-09.
  4. ^ "Watches, Warnings & Advisories—Flash Flood Warning". National Weather Service. Archived from the original on 2008-01-11. Retrieved 2007-06-25.
  5. ^ "A Preparedness Guide to flash floods #1 weather-related killer in the United States". U.S. Department of Commerce, National Oceanic and Atmospheric Administration National Weather Service, Federal Emergency Management Agency, American Red Cross. July 1992. Retrieved 2007-06-25.
  6. ^ "Turn Around Don't Drown". Retrieved 2007-06-25.
  7. ^ Campos, Priscila Celebrini de Oliveira; Paz, Igor (2020). "Spatial Diagnosis of Rain Gauges' Distribution and Flood Impacts: Case Study in Itaperuna, Rio de Janeiro—Brazil". Water. 12 (4): 1120. doi:10.3390/w12041120.
  8. ^ McGuire, Thomas (2004). "Weather Hazards and the Changing Atmosphere" (PDF). Earth Science: The Physical Setting. Amsco School Pubns Inc. p. 571. ISBN 0-87720-196-X. Archived from the original (PDF) on 2008-06-25. Retrieved 2008-07-17.
  9. ^ Jahns, R.H. (1949). "Desert floods" (PDF). Engineering and Science. 12 (8): 10–14. Retrieved 17 July 2021.
  10. ^ Smith, James A.; Baeck, Mary Lynn; Yang, Long; Signell, Julia; Morin, Efrat; Goodrich, David C. (December 2019). "The Paroxysmal Precipitation of the Desert: Flash Floods in the Southwestern United States". Water Resources Research. 55 (12): 10218–10247. doi:10.1029/2019WR025480.
  11. ^ Jump up to: a b Diakakis M.; Deligiannakis G.; Antoniadis Z.; Melaki M.; Katsetsiadou K.N.; Andreadakis E.; Spyrou N.I. & Gogou M. (2020). "Proposal of a flash flood impact severity scale for the classification and mapping of flash flood impacts". Journal of Hydrology. 590: 125452. Bibcode:2020JHyd..59025452D. doi:10.1016/j.jhydrol.2020.125452.
  12. ^ Calianno, Martin; Ruin, Isabelle; Gourley, Jonathan J. (January 2013). "Supplementing flash flood reports with impact classifications". Journal of Hydrology. 477: 1–16. doi:10.1016/j.jhydrol.2012.09.036.
  13. ^ Špitalar, Maruša; Gourley, Jonathan J.; Lutoff, Celine; Kirstetter, Pierre-Emmanuel; Brilly, Mitja; Carr, Nicholas (November 2014). "Analysis of flash flood parameters and human impacts in the US from 2006 to 2012". Journal of Hydrology. 519: 863–870. doi:10.1016/j.jhydrol.2014.07.004.
  14. ^ Brilly, Mitja (2001). "The Integrated Approach to Flash Flood Management". Coping With Flash Floods: 103–113. doi:10.1007/978-94-010-0918-8_12.
  15. ^ Labib, Tarik M. (September 1981). "Soil erosion and total denudation due to flash floods in the Egyptian eastern desert". Journal of Arid Environments. 4 (3): 191–202. doi:10.1016/S0140-1963(18)31560-X.
  16. ^ Marchi, Lorenzo; Cavalli, Marco; Amponsah, William; Borga, Marco; Crema, Stefano (November 2016). "Upper limits of flash flood stream power in Europe". Geomorphology. 272: 68–77. doi:10.1016/j.geomorph.2015.11.005.
  17. ^ Hattori, Yoko; Nagai, Keisuke; Ashikari, Motoyuki (February 2011). "Rice growth adapting to deepwater". Current Opinion in Plant Biology. 14 (1): 100–105. doi:10.1016/j.pbi.2010.09.008.
  18. ^ Shailes, Sarah (25 February 2014). "How flooding affects plants". Plant Scientist. Retrieved 14 July 2020.
  19. ^ Tamang, Bishal; Fukao, Takeshi (17 December 2015). "Plant Adaptation to Multiple Stresses during Submergence and Following Desubmergence". International Journal of Molecular Sciences. 16 (12): 30164–30180. doi:10.3390/ijms161226226. PMC 4691168.
  20. ^ "Making Sense of Nepal's Seti River Disaster". earthobservatory.nasa.gov. 24 January 2014.
  21. ^ "At least 105 dead as torrential rains inundate southern Russia". Los Angeles Times. 2012-07-07. Retrieved 2012-07-07.
  22. ^ Kuzmin, Andrey (2012-07-08). "Russia's Putin demands answers after floods leave 150 dead". msnbc.com. Reuters. Archived from the original on 2012-07-08. Retrieved 2012-07-08.
  23. ^ "Uttarakhand: More than 5000 dead; 2000 still stranded". Business Standard. 2013-06-28. Retrieved 2013-06-28.
  24. ^ Waseem, Fatimah. "Ellicott City flood prompts call for nine-month freeze on development".
  25. ^ report, Advocate staff. "What caused the historic August 2016 flood, and what are the odds it could happen again?". The Advocate. Retrieved 2018-01-27.
  26. ^ "9 YOUTH DEAD IN SOUTHERN ISRAEL FLASH FLOODS". Retrieved 2018-04-26.
  27. ^ Miller, Michael E.; Shapira, Ian (May 28, 2018). "'Washed away real quick': Missing Md. man was trying to help woman trapped by flood". The Washington Post.
  28. ^ ecodellojonio.it, ed. (21 August 2018). "Tragedia raganello: allerta gialla ignorata, tragedia evitabile" (in Italian). Retrieved 2018-08-21.
  29. ^ bbc.com, ed. (11 October 2018). "Search for missing after 15 killed in Europe floods". BBC News. Retrieved 2018-10-12.
  30. ^ "Flash Floods Turn Deadly In Southwest France's Aude Region". NPR.org. Retrieved 2020-03-02.
  31. ^ "Death toll rises to 21 in Dead Sea flash floods". The Jordan Times. 2018-10-26.
  32. ^ "Floodwaters deluge Iran, killing at least 23, after a month's worth of rain turns roads into rivers".
  33. ^ "Afghanistan Flooding Kills at Least 16, Official Says". AP via The Weather Channel. Retrieved 2019-03-29.

Further reading[]

  • Schmittner, Karl-Erich; Pierre Giresse (August 1996). "Modelling and application of the geomorphic and environmental controls on flash flood flow". Geomorphology. 16 (4): 337–47. Bibcode:1996Geomo..16..337S. doi:10.1016/0169-555X(96)00002-5.

External links[]

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