Flooding in Bom Princípio of the Caí River in Brazil during July 2020
Flooding in Bom Princípio of the Caí River in Brazil during July 2020

Urban flooding is the inundation of land or property in a built environment, particularly in more densely populated areas, caused by rainfall overwhelming the capacity of drainage systems, such as storm sewers. Although sometimes triggered by events such as flash flooding or snowmelt, urban flooding is a condition, characterized by its repetitive and systemic impacts on communities, that can happen regardless of whether or not affected communities are located within designated floodplains or near any body of water.[1] Aside from potential overflow of rivers and lakes, snowmelt, stormwater or water released from damaged water mains may accumulate on property and in public rights-of-way, seep through building walls and floors, or backup into buildings through sewer pipes, toilets and sinks.

In urban areas, flood effects can be exacerbated by existing paved streets and roads, which increase the speed of flowing water. Impervious surfaces prevent rainfall from infiltrating into the ground, thereby causing a higher surface run-off that may be in excess of local drainage capacity.[2]

The flood flow in urbanized areas constitutes a hazard to both the population and infrastructure. Some recent catastrophes include the inundations of Nîmes (France) in 1998 and Vaison-la-Romaine (France) in 1992, the flooding of New Orleans (USA) in 2005, and the flooding in Rockhampton, Bundaberg, Brisbane during the 2010–2011 summer in Queensland (Australia). Flood flows in urban environments have been studied relatively recently despite many centuries of flood events.[3] Some recent research has considered the criteria for safe evacuation of individuals in flooded areas.[4]

Background

People kayaking down a street in Mid-City New Orleans following flooding in 2019
People kayaking down a street in Mid-City New Orleans following flooding in 2019

There are several types of flooding, including pluvial (flooding caused by heavy rain), fluvial (caused by a nearby river overflowing its banks), and coastal flooding (often caused by storm surges). Different types of urban flooding create different impacts and require different mitigation strategies.

Links to climate change

Many of the common causes of urban flooding, including storm surges, heavy precipitation, and river overflow, are expected to increase in frequency and severity as climate change intensifies and causes increases in ocean and river levels.[5] In particular, erratic rainfall patterns are expected to increase the frequency and severity of both pluvial flooding (as excessive amounts of rainfall in urban areas and cannot be adequately absorbed by existing drainage systems and pervious areas) and fluvial flooding (as excessive rainfall over a river can cause flooding and overflow, either where it occurs or downstream along the path of the river). The frequencies and severities of extreme storm events, including hurricanes and other types of tropical cyclones, are also expected to increase,[6] raising the risk of storm surges and the potential for heavy rainfall and increasing flooding-related damages by up to US$54B annually.[7] Additionally, due to the geographic distribution of developing urban areas, the land area potentially exposed to climate change-related flooding is expected to increase significantly.[8]

Case studies

One of the most well known at-risk urban areas in the United States is New Orleans. Because of its coastal location and low elevation, the city is prone to flooding due to tropical storms, including cyclones and hurricanes and is particularly vulnerable to changes in sea level or storm frequency. In 2005, Hurricane Katrina caused more than 1800 deaths and US$170B in damages.[9] After Katrina, additional flood protections were built with a changing climate in mind; these protections have proved effective in reducing damages due to subsequent extreme weather events, such as Hurricane Ida.[10]

During the summer of 2021, Hurricanes Henri and Ida caused significant flooding in many cities along the east coast of the United States.[11][12] In particular, New York City experienced record levels of rainfall, prompting many to question whether the city should implement additional flood protection measures in anticipation of potential future flood events.[13] In September 2021, the New York City mayoral office released a new rainfall preparedness plan.[14]

Impacts

Some of the most obvious impacts of urban flooding are those to human life and to property damage. In 2020, floods caused an estimated 6,000 deaths and caused US$51.3B in damages globally.[15]

Urban flooding also impacts critical public services, including public transportation systems.[16][17] Traffic congestion can be worsened by urban flood events,[18] impacting ease of access to transportation, as well as the ability of emergency services to operate effectively.

Urban flooding can also create far-reaching supply chain issues,[19][20] which can create significant interruptions in the availability of goods and services, as well as financial losses for businesses.

Economic impacts

Urban flooding has significant economic implications. In the US, industry experts estimate that wet basements can lower property values by 10%-25% and are cited among the top reasons for not purchasing a home.[21] According to the U.S Federal Emergency Management Agency (FEMA), almost 40% of small businesses never reopen their doors following a flooding disaster.[22] In the UK, urban flooding is estimated to cost £270 million a year in England and Wales; 80,000 homes are at risk.[23]

A study of Cook County, Illinois, identified 177,000 property damage insurance claims made across 96% of the county's ZIP codes over a five-year period from 2007-2011. This is the equivalent of one in six properties in the County making a claim. Average payouts per claim were $3,733 across all types of claims, with total claims amounting to $660 million over the five years examined.[21]

Despite concerted efforts, many communities lack the funds to fully address these issues and often seek funds elsewhere. Numerous watersheds within Los Angeles County, California do not meet state water quality standards, despite spending $100 million a year on clean water programs to combat issues such as urban runoff. To combat this problem, officials have introduced a measure that would assess a fee to homeowners and local businesses in an attempt to raise $290 million for effective urban runoff management.[24]

Modeling

Flood modeling is often conducted in a very localized fashion, with hydrological models created for individual municipalities and incorporating details about buildings, infrastructure, vegetation, land use, and drainage systems.[25] This localized modeling can be very useful, especially when paired with historical data, in predicting which specific locations (e.g. streets or intersections) will be the most impacted during a flood event and can be helpful in designing effective mitigation systems specific to local needs.

Flood flows in urban environments have been investigated relatively recently despite many centuries of flood events.[26] Some researchers mentioned the storage effect in urban areas. Several studies looked into the flow patterns and redistribution in streets during storm events and the implication in terms of flood modelling.[27] Some recent research considered the criteria for safe evacuation of individuals in flooded areas.[28] But some recent field measurements during the 2010–2011 Queensland floods showed that any criterion solely based upon the flow velocity, water depth or specific momentum cannot account for the hazards caused by the velocity and water depth fluctuations.[26] These considerations ignore further the risks associated with large debris entrained by the flow motion.[28]

Global climate models usually do not include detailed local predictions
Global climate models usually do not include detailed local predictions

Modeling of climate impacts, on the other hand, is often done from a "top-down", global perspective. While these models can be helpful in predicting worldwide effects of global warming and in raising awareness about large-scale impacts, their spatial resolution is often limited to 25 km or more, making them less helpful for local planners in mitigating the effects of climate change on a street-by-street scale.[29]

Some advocate for an integration of localized hydrological modeling with larger-scale climate modeling, claiming that such integration allows the benefits of both forms of modeling to be realized simultaneously and creates the potential for modeling flooding due to climate change in a way that allows planners to design specific strategies to mitigate it at the local level.[30]

Management

Comparing the natural and urban water cycle and streetscapes in conventional and Blue-Green Cities
Comparing the natural and urban water cycle and streetscapes in conventional and Blue-Green Cities

Integrated urban water management (IUWM) is the practice of managing freshwater, wastewater, and storm water as components of a basin-wide management plan. It builds on existing water supply and sanitation considerations within an urban settlement by incorporating urban water management within the scope of the entire river basin.[31] IUWM is commonly seen as a strategy for achieving the goals of Water Sensitive Urban Design. IUWM seeks to change the impact of urban development on the natural water cycle, based on the premise that by managing the urban water cycle as a whole; a more efficient use of resources can be achieved providing not only economic benefits but also improved social and environmental outcomes. One approach is to establish an inner, urban, water cycle loop through the implementation of reuse strategies. Developing this urban water cycle loop requires an understanding both of the natural, pre-development, water balance and the post-development water balance. Accounting for flows in the pre- and post-development systems is an important step toward limiting urban impacts on the natural water cycle.[32]

IUWM within an urban water system can also be conducted by performance assessment of any new intervention strategies by developing a holistic approach which encompasses various system elements and criteria including sustainability type ones in which integration of water system components including water supply, waste water and storm water subsystems would be advantageous.[33] Simulation of metabolism type flows in urban water system can also be useful for analysing processes in urban water cycle of IUWM.[33][34]

Mitigation

Gray infrastructure

One traditional urban flooding management strategy is gray infrastructure, which is a set of infrastructure types (including dams and seawalls) traditionally constructed of concrete or other impervious materials and designed to prevent the flow of water. While gray infrastructure can be effective in preventing flooding-related damage[35] and can be economically valuable,[36] some models suggest that gray infrastructure may become less effective at preventing flood-related impacts in urban areas in the future as climate change causes flooding intensity and frequency to increase.[37]

Green infrastructure

A schematic showing how green infrastructure and water management can be integrated
A schematic showing how green infrastructure and water management can be integrated

An alternative to gray infrastructure is green infrastructure, which refers to a set of strategies for absorbing and storing stormwater at or close to the location where it falls. Green infrastructure includes many types of vegetation, large open areas with pervious surfaces, and even rainwater collection devices.[38] Green infrastructure may prove to be an effective and cost-efficient way to reduce the extent of urban flooding.[39]

Drainage systems

One way urban flooding is commonly mitigated is via urban drainage systems, which transport storm water away from streets and businesses and into appropriate storage and drainage areas. While urban drainage systems help municipalities manage flooding and can be scaled up as population and urban extent increase, these systems may not be sufficient to mitigate additional future flooding due to climate change.[40]

Land use

Since the ratio of pervious to impervious surfaces across an area is important in flooding management, understanding and altering land use and the proportion of land allocated to different purposes/use types is important in flood management planning.[41][42] In particular, increasing the percent of land dedicated to open, vegetated space can be helpful in providing an absorption and storage area for storm runoff.[43] These areas can often be integrated with existing urban amenities, such as parks and golf courses. Increasing the pervious surface fraction of an urban area (e.g. by planting green walls/roofs or using alternative pervious construction materials) can also help de-risk climate-linked flood events.[44][45]

See also

References

  1. ^ Center for Neighborhood Technology, Chicago IL, "The Prevalence and Cost of Urban Flooding", May 2013
  2. ^ Urban adaptation to climate change in Europe - EEA
  3. ^ Brown, Richard; Chanson, Hubert; McIntosh, Dave; Madhani, Jay (2011). Turbulent Velocity and Suspended Sediment Concentration Measurements in an Urban Environment of the Brisbane River Flood Plain at Gardens Point on 12–13 January 2011. Hydraulic Model Report No. CH83/11. p. 120. ISBN 978-1-74272-027-2.
  4. ^ Chanson, H., Brown, R., McIntosh, D. (26 June 2014). "Human body stability in floodwaters: The 2011 flood in Brisbane CBD". In L. Toombes (ed.). Hydraulic structures and society - Engineering challenges and extremes (PDF). Brisbane, Australia: Proceedings of the 5th IAHR International Symposium on Hydraulic Structures (ISHS2014). pp. 1–9. doi:10.14264/uql.2014.48. ISBN 978-1-74272-115-6.((cite book)): CS1 maint: uses authors parameter (link)
  5. ^ Symonds, Michael (2021-08-10). "Faculty Opinions recommendation of IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change". doi:10.3410/f.740620545.793587812. S2CID 242570539. Retrieved 2021-10-30. ((cite journal)): Cite journal requires |journal= (help)
  6. ^ Knutson, Thomas R.; McBride, John L.; Chan, Johnny; Emanuel, Kerry; Holland, Greg; Landsea, Chris; Held, Isaac; Kossin, James P.; Srivastava, A. K.; Sugi, Masato (2010-02-21). "Tropical cyclones and climate change". Nature Geoscience. 3 (3): 157–163. Bibcode:2010NatGe...3..157K. doi:10.1038/ngeo779. ISSN 1752-0894.
  7. ^ Mendelsohn, Robert; Emanuel, Kerry; Chonabayashi, Shun; Bakkensen, Laura (2012-01-15). "The impact of climate change on global tropical cyclone damage". Nature Climate Change. 2 (3): 205–209. Bibcode:2012NatCC...2..205M. doi:10.1038/nclimate1357. ISSN 1758-678X.
  8. ^ Anderson, Tiffany R.; Fletcher, Charles H.; Barbee, Matthew M.; Romine, Bradley M.; Lemmo, Sam; Delevaux, Jade M.S. (2018-09-27). "Modeling multiple sea level rise stresses reveals up to twice the land at risk compared to strictly passive flooding methods". Scientific Reports. 8 (1): 14484. Bibcode:2018NatSR...814484A. doi:10.1038/s41598-018-32658-x. ISSN 2045-2322. PMC 6160426. PMID 30262891.
  9. ^ Office, U. S. Government Accountability. "Natural Disasters: Economic Effects of Hurricanes Katrina, Sandy, Harvey, and Irma". www.gao.gov. Retrieved 2021-11-07.
  10. ^ "Engineers Bent the Rules, and May Have Saved New Orleans". Time. Retrieved 2021-11-07.
  11. ^ By <a href="/profiles/fernando-alfonso-iii">Fernando Alfonso III</a>, Mike Hayes, <a href="/profiles/judson-jones">Judson Jones</a> and <a href="/profiles/meg-wagner">Meg Wagner</a> (2021-08-22). "August 22, 2021 Tropical Storm Henri makes landfall in the Northeast". CNN. Retrieved 2021-11-07.((cite web)): CS1 maint: multiple names: authors list (link)
  12. ^ Analysis by Angela Dewan, International Climate Editor (2 September 2021). "Analysis: Ida turns New York City into a front line of climate change-supercharged weather". CNN. Retrieved 2021-11-07. ((cite web)): |author= has generic name (help)
  13. ^ McKinley, Jesse; Rubinstein, Dana; Mays, Jeffery C. (2021-09-03). "The Storm Warnings Were Dire. Why Couldn't New York Be Protected?". The New York Times. ISSN 0362-4331. Retrieved 2021-11-07.
  14. ^ Times, The New York (2021-09-04). "Video: New York's Mayor Outlines Rain-Preparedness Plan". The New York Times. ISSN 0362-4331. Retrieved 2021-11-07.
  15. ^ Disasters, Centre for Research on the Epidemiology of; Reduction, UN Office for Disaster Risk (2021). "2020 The Non-Covid year in disasters: Global trends and perspectives". ((cite journal)): Cite journal requires |journal= (help)
  16. ^ Suarez, Pablo; Anderson, William; Mahal, Vijay; Lakshmanan, T.R. (May 2005). "Impacts of flooding and climate change on urban transportation: A systemwide performance assessment of the Boston Metro Area". Transportation Research Part D: Transport and Environment. 10 (3): 231–244. doi:10.1016/j.trd.2005.04.007. ISSN 1361-9209.
  17. ^ Chang, Heejun; Lafrenz, Martin; Jung, Il-Won; Figliozzi, Miguel; Platman, Deena; Pederson, Cindy (2010-08-31). "Potential Impacts of Climate Change on Flood-Induced Travel Disruptions: A Case Study of Portland, Oregon, USA". Annals of the Association of American Geographers. 100 (4): 938–952. doi:10.1080/00045608.2010.497110. ISSN 0004-5608. S2CID 16751304.
  18. ^ Zhu, Jingxuan; Dai, Qiang; Deng, Yinghui; Zhang, Aorui; Zhang, Yingzhe; Zhang, Shuliang (2018-05-10). "Indirect Damage of Urban Flooding: Investigation of Flood-Induced Traffic Congestion Using Dynamic Modeling". Water. 10 (5): 622. doi:10.3390/w10050622. ISSN 2073-4441.
  19. ^ Ohmori, Shunichi; Yoshimoto, Kazuho (2013-06-30). "A Framework of Managing Supply Chain Disruption Risks Using Network Reliability". Industrial Engineering and Management Systems. 12 (2): 103–111. doi:10.7232/iems.2013.12.2.103. ISSN 1598-7248.
  20. ^ Jongman, Brenden (2018-05-29). "Effective adaptation to rising flood risk". Nature Communications. 9 (1): 1986. Bibcode:2018NatCo...9.1986J. doi:10.1038/s41467-018-04396-1. ISSN 2041-1723. PMC 5974412. PMID 29844334.
  21. ^ a b "The Prevalence and Cost of Urban Flooding." May 2013, Center for Neighborhood Technology, Chicago IL.
  22. ^ Federal Emergency Management Agency (U.S.). "Protecting Your Businesses," last updated March, 2013, http://www.fema.gov/protecting-yourbusinesses Archived 2013-09-17 at archive.today
  23. ^ Parliamentary Office of Science and Technology, London, UK. "Urban Flooding." Postnote 289, July 2007
  24. ^ Sewell, Abby (2013-01-03). "County seeks parcel fee to pay for projects to combat urban runoff". Los Angeles Times.
  25. ^ Rosenzweig, B. R.; Cantis, P. Herreros; Kim, Y.; Cohn, A.; Grove, K.; Brock, J.; Yesuf, J.; Mistry, P.; Welty, C.; McPhearson, T.; Sauer, J. (2021). "The Value of Urban Flood Modeling". Earth's Future. 9 (1): e2020EF001739. Bibcode:2021EaFut...901739R. doi:10.1029/2020EF001739. ISSN 2328-4277. S2CID 234311646.
  26. ^ a b Brown, Richard; Chanson, Hubert; McIntosh, Dave; Madhani, Jay (2011). Turbulent Velocity and Suspended Sediment Concentration Measurements in an Urban Environment of the Brisbane River Flood Plain at Gardens Point on 12–13 January 2011. Hydraulic Model Report No. CH83/11. Brisbane, Australia: The University of Queensland, School of Civil Engineering. ISBN 978-1-74272-027-2.[page needed]
  27. ^ Werner, M.G.F.; Hunter, N.M.; Bates, P.D. (November 2005). "Identifiability of distributed floodplain roughness values in flood extent estimation". Journal of Hydrology. 314 (1–4): 139–157. Bibcode:2005JHyd..314..139W. doi:10.1016/j.jhydrol.2005.03.012.
  28. ^ a b Chanson, Hubert; Brown, R.; McIntosh, D. (2014). "Human body stability in floodwaters: The 2011 flood in Brisbane CBD" (PDF). Hydraulic structures and society - Engineering challenges and extremes. pp. 1–9. doi:10.14264/uql.2014.48. ISBN 978-1-74272-115-6.
  29. ^ Setzer, Maria. "Climate Modeling". www.gfdl.noaa.gov. Retrieved 2021-11-07.
  30. ^ Cheng, Chingwen; Yang, Y.C. Ethan; Ryan, Robert; Yu, Qian; Brabec, Elizabeth (November 2017). "Assessing climate change-induced flooding mitigation for adaptation in Boston's Charles River watershed, USA". Landscape and Urban Planning. 167: 25–36. doi:10.1016/j.landurbplan.2017.05.019. ISSN 0169-2046.
  31. ^ Tucci, C., Goldenfum, J.A., Parkinson J.N. (2009). 978-92-3-104065-8 "Integrated Urban Water Management: Humid Tropics". CRC Press. p. 2. Retrieved 2009-09-18. ((cite web)): Check |url= value (help)CS1 maint: multiple names: authors list (link)
  32. ^ Barton, A.B. (2009). "Advancing IUWM through an understanding of the urban water balance". Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). Retrieved 2009-09-14.
  33. ^ a b Behzadian, K; Kapelan, Z (2015). "Advantages of integrated and sustainability based assessment for metabolism based strategic planning of urban water systems" (PDF). Science of the Total Environment. 527–528: 220–231. Bibcode:2015ScTEn.527..220B. doi:10.1016/j.scitotenv.2015.04.097. hdl:10871/17351. PMID 25965035.
  34. ^ Behzadian, k; Kapelan, Z (2015). "Modelling metabolism based performance of an urban water system using WaterMet2" (PDF). Resources, Conservation and Recycling. 99: 84–99. doi:10.1016/j.resconrec.2015.03.015. hdl:10871/17108.
  35. ^ "Water security: Gray or green?". Science. 349 (6248): 584. 2015-08-07. doi:10.1126/science.349.6248.584-a. ISSN 0036-8075. PMID 26250669.
  36. ^ Davlasheridze, Meri; Fan, Qin (2019-08-07). "Valuing Seawall Protection in the Wake of Hurricane Ike". Economics of Disasters and Climate Change. 3 (3): 257–279. doi:10.1007/s41885-019-00045-z. ISSN 2511-1280. S2CID 201297569.
  37. ^ Kim, Yeowon; Eisenberg, Daniel A.; Bondank, Emily N.; Chester, Mikhail V.; Mascaro, Giuseppe; Underwood, B. Shane (2017-10-26). "Fail-safe and safe-to-fail adaptation: decision-making for urban flooding under climate change". Climatic Change. 145 (3–4): 397–412. Bibcode:2017ClCh..145..397K. doi:10.1007/s10584-017-2090-1. ISSN 0165-0009. S2CID 158494951.
  38. ^ US EPA, OW (2015-09-30). "What is Green Infrastructure?". www.epa.gov. Retrieved 2021-11-07.
  39. ^ Chen, Jingqiu; Liu, Yaoze; Gitau, Margaret W.; Engel, Bernard A.; Flanagan, Dennis C.; Harbor, Jonathan M. (2019-05-15). "Evaluation of the effectiveness of green infrastructure on hydrology and water quality in a combined sewer overflow community". Science of the Total Environment. 665: 69–79. Bibcode:2019ScTEn.665...69C. doi:10.1016/j.scitotenv.2019.01.416. ISSN 0048-9697. PMID 30772580. S2CID 73457016.
  40. ^ Skougaard Kaspersen, Per; Høegh Ravn, Nanna; Arnbjerg-Nielsen, Karsten; Madsen, Henrik; Drews, Martin (2017-08-18). "Comparison of the impacts of urban development and climate change on exposing European cities to pluvial flooding". Hydrology and Earth System Sciences. 21 (8): 4131–4147. Bibcode:2017HESS...21.4131S. doi:10.5194/hess-21-4131-2017. ISSN 1607-7938. S2CID 54025209.
  41. ^ Neupane, Barsha; Vu, Tue M.; Mishra, Ashok K. (2021-09-07). "Evaluation of land-use, climate change, and low-impact development practices on urban flooding". Hydrological Sciences Journal. 66 (12): 1729–1742. doi:10.1080/02626667.2021.1954650. ISSN 0262-6667. S2CID 238241352.
  42. ^ Dammalage, T. L.; Jayasinghe, N. T. (2019-04-10). "Land-Use Change and Its Impact on Urban Flooding: A Case Study on Colombo District Flood on May 2016". Engineering, Technology & Applied Science Research. 9 (2): 3887–3891. doi:10.48084/etasr.2578. ISSN 1792-8036. S2CID 155967894.
  43. ^ Kim, Hyomin; Lee, Dong-Kun; Sung, Sunyong (2016-01-30). "Effect of Urban Green Spaces and Flooded Area Type on Flooding Probability". Sustainability. 8 (2): 134. doi:10.3390/su8020134. ISSN 2071-1050.
  44. ^ BOYD, M. J.; BUFILL, M. C.; KNEE, R. M. (December 1993). "Pervious and impervious runoff in urban catchments". Hydrological Sciences Journal. 38 (6): 463–478. doi:10.1080/02626669309492699. ISSN 0262-6667.
  45. ^ Liu, Wen; Chen, Weiping; Peng, Chi (November 2014). "Assessing the effectiveness of green infrastructures on urban flooding reduction: A community scale study". Ecological Modelling. 291: 6–14. doi:10.1016/j.ecolmodel.2014.07.012. ISSN 0304-3800. S2CID 83502965.