Urban Resilience to Floods in Coastal Cities Duy, Phan; Chapman, Lee; Tight, Miles; Thoung, L; Linh, P
Total Page:16
File Type:pdf, Size:1020Kb
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Birmingham Research Portal Urban Resilience to Floods in Coastal Cities Duy, Phan; Chapman, Lee; Tight, Miles; Thoung, L; Linh, P DOI: 10.1061/(ASCE)UP.1943-5444.0000419 License: None: All rights reserved Document Version Peer reviewed version Citation for published version (Harvard): Duy, P, Chapman, L, Tight, M, Thoung, L & Linh, P 2018, 'Urban Resilience to Floods in Coastal Cities: Challenges and Opportunities for Ho Chi Minh City and other Emerging Cities in Southeast Asia', Journal of the Urban Planning and Development Division, ASCE, vol. 144, no. 1, 05017018. https://doi.org/10.1061/(ASCE)UP.1943-5444.0000419 Link to publication on Research at Birmingham portal Publisher Rights Statement: Final version of the document is available at: https://dx.doi.org/10.1061/(ASCE)UP.1943-5444.0000419 General rights Unless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or the copyright holders. The express permission of the copyright holder must be obtained for any use of this material other than for purposes permitted by law. •Users may freely distribute the URL that is used to identify this publication. •Users may download and/or print one copy of the publication from the University of Birmingham research portal for the purpose of private study or non-commercial research. •User may use extracts from the document in line with the concept of ‘fair dealing’ under the Copyright, Designs and Patents Act 1988 (?) •Users may not further distribute the material nor use it for the purposes of commercial gain. Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive. If you believe that this is the case for this document, please contact [email protected] providing details and we will remove access to the work immediately and investigate. Download date: 01. Feb. 2019 1 Urban Resilience to Floods in Coastal Cities: Challenges and Opportunities for Ho Chi Minh City and other 2 Emerging Cities in Southeast Asia 3 4 P. N. Duy1,*, L. Chapman2, M. Tight3, L. V. Thuong4, P. N. Linh5, 5 1 Doctoral Researcher, School of Geography, Earth & Environmental Sciences, University of Birmingham, UK 6 2 Professor, School of Geography, Earth & Environmental Sciences, University of Birmingham, UK 7 3 Professor, School of Civil Engineering, University of Birmingham, UK 8 4 Doctor, Ho Chi Minh City University of Architecture, Vietnam 9 5 Urban planner, MA., Ho Chi Minh City, Vietnam. 10 * Corresponding author 11 12 Abstract 13 Flooding is a hazard in many cities despite the presence of flood protection systems. However, recent losses and damages due to 14 flooding in many coastal cities have indicated that the increasing volatility of natural disasters and flood events are now 15 exceeding present day design considerations. By comparing and deriving common lessons from case studies in New Orleans, 16 Manila and Bangkok, this paper focuses on the extent to which coastal cities are becoming more vulnerable to flooding and 17 argues that broader urban resilience in the planning process now has an increasing role to play alongside traditional flood 18 defences. Given the present speed of development in SE Asia, there are opportunities for these ideas to be readily and rapidly 19 incorporated into development plans to reduce the severity of increasing flood events in the region. 20 21 Keywords 22 Urban resilience, flood vulnerability, spatial planning and management, coastal city 23 24 1 25 Introduction 26 "I urge local authorities to accelerate all efforts take cities safer to prevent the loss of lives and assets" (Ban Ki- 27 moon, 2009; cited in United Nations-Habitat, 2009). 28 29 Floods in urban areas continue to make headline news throughout the world with the increasing frequency and 30 severity of events often attributed to climate change (Zevenbergen, 2008). In a review of significant events from 31 1980 to 2009, Doocy et al. (2013) attributed flooding to be the cause of 539,811 deaths, whilst affecting a further 2.8 32 billion people all over the world. Whilst extreme events can cause long-term devastation, even small floods can 33 have a significant impact on urban activities. The standard response to mitigate against flooding is via flood defense 34 systems. These can take on many forms - coastal dike, river embankment, dam and levee system, but they typically 35 have design constraints (e.g. built to withstand a 100-year flood). There is clearly a need to balance probability with 36 cost benefit, but in a changing climate, the likelihood of extreme events continues to increase and this has meant in 37 recent years that flood protection systems have not always proved effective in dealing with the disastrous effects of 38 large scale flooding. This is demonstrated by many recent examples of ‘protected’ cities worldwide which have 39 subsequently suffered substantial losses to floods; in America (New Orleans 2005), Europe (Lancaster – United 40 Kingdom 2015), China (Guangzhou-Guangdong, 2007), Australia (Brisbane 2011) as well as a number of cities in 41 South East (SE) Asia (Manila – Philippines 2009, Bangkok - Thailand 2011 and Ho Chi Minh City – Vietnam 42 2015) 43 44 The flooding problem can be particularly acute in coastal cities. Of the 20 largest cities in the world, 13 are located 45 on the coast (World Bank, hereafter called WB, 2010), with more than 20% of the world’s population now living in 46 the coastal zone (du Gommes et al. 1997; Brooks et al. 2006). The low-elevation coastal zone (LECZ) normally 47 refers to land that is less than 10 meters above sea level (Vafeidis et al., 2011, International Panel on Climate 48 Change - IPPC 2014). Whilst tidal flooding and storm surges have always been a hazard in the LECZ, vulnerability 49 increases in a changing climate due to sea-level rise (Neumann et al., 2015), which is now estimated to be 74cm by 50 the end of 21st century (IPPC, 2014). Cities in the LECZ are often also located on estuaries or at the mouths of 51 major rivers. This means the threat of flooding in this zone can also be fluvial (or often a combination of both). An 52 illustration of this is the location of Manila city, based on the western shore of Manila bay and through which the 53 Pasig and San Juan River traverse. 54 55 As the world becomes increasingly urbanized, pressure to increase development in the LECZ is also increasing, 56 resulting in larger (or new) settlements facing flooding hazards (McGranahan et al., 2007). Ultimately, rapid 57 urbanisation is producing a concentration of people assets in areas prone to floods, particularly built-up areas along 58 major bodies (Zevenbergen, 2008). Such rapid development further contributes to the problem because of weak 59 planning regulations in the wetlands, forests, floodplains and mangroves adjacent to the urban areas (often located in 60 the LECZ) which provide a natural defense to flooding (United Nations - UN, 2013). For example, in a study of 76 61 developing countries, Dasgupta et al. (2012) highlights the gradual loss of coastal wetland through human actions 62 resulting from urban expansion. Driven by economic growth, urban enlargement results in a concentration of 63 citizens and assets outside of former centers. Enlargement is not new and can be traced back to the 19th century, 64 where the industrial revolution prompted the expansion of towns and cities (Hall and Jones, 2011). This trend has 65 continued to this day and now over 50% of the world’s population is urbanized (UN, 2014). However, this growth 66 is becoming increasingly difficult to accommodate and many cities have now expanded their territory without 67 thorough consideration of the risks to living environment. Angel et al. (2005) examined the processes of global 68 urban expansion and concluded that population had not actually been distributed according to the plans approved in 69 almost all of the 90 cities surveyed; while Gentlemen (2007) relied on the estimation of the UN stated that only 5% 70 of new developments had been exactly implemented alongside to their existing plans. 71 72 In this paper, the term “coastal city” is used to define an urban area where settlement has occurred on the LECZ and 73 is vulnerable to flooding (which may be both coastal and fluvial). According to Population Division of the United 74 Nations (1993, cited in Nicholls, 1995), there has been a remarkable increase in the number of coastal mega-cities, 75 which have the potential to be impacted by sea-level rise, from 13 in 1990 to 20 in 2010. Indeed, this feeds into a 76 general trend of global cities becoming more vulnerable to disasters due to spatial development related to sprawling 77 sub-urbanization widespread to areas prone to environmental hazards (National Research Council of The National 78 Academies of the United States, 2006), creating a spatial redistribution of the population into vulnerable areas 79 (Chang et al., 2012). As such, due to the rapid development experienced over the last few decades in SE Asia, a 80 large concentration of increasingly vulnerable coastal cities has emerged in this region. Here, countries are targeting 81 the economic growth associated with urbanisation, but this now means that urban expansion has spread to areas that 82 are increasingly at risk from flooding and this is compromising the adaptive capacity of the broader city to cope with 83 natural risks which is essential for the long-term planning for urban development (UN, 2013) but frequently 84 overlooked by local government.