Global Assessment Report on Disaster Risk Reduction 2015
Making development sustainable: The future of disaster risk management

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The urban population living in informal settlements has actually grown over the last two decades, from around 650 million in 1990 to more than 860 million in 2012 (UN-Habitat, 2013).4 This growth has severely undermined the relevance of the related target in the Millennium Development Goals: “By 2020, to have achieved a significant improvement in the lives of at least 100 million slum dwellers”.5 At the same time, local and national governments often neglect to define, classify or quantify informal settlements and the corresponding risks and demands of their inhabitants (Sarmiento et al., 2014

Sarmiento Prieto, Juan Pablo, Gabriela Hoberman and Richard Stuart Olson. 2014,Urban Development and Disaster Risk: Formality and Informality, Working Paper. Disaster Risk Reduction in the Americas Project. Latin American and Caribbean Center, Florida International University, Miami. November 2010.. .
In some areas in Karachi, Pakistan (Hasan et al., 2010

Hasan, Arif, Asiya Sadiq and Suneela Ahmed. 2010,Planning for high density in low-income settlements: Four case studies from Karachi, Human Settlements Working Paper Series. Urbanization and emerging population issues - 3. UNFPA, IIED, March 2010.. .
), there are more than 4,000 inhabitants per hectare (2.4 m
2 of space per inhabitant), compared to 200 persons per hectare (50m2 per inhabitant) in high-income areas. In Tanzania, around 70 per cent of Dar es Salaam’s population lives in low-quality housing at risk of regular flooding (Kahn, 2014

Kahn, Matthew E. 2014,Sustainable and Smart Cities, Policy Research Working Paper 6878. The World Bank Sustainable Development Network, Urban and Disaster Management Department. May 2014. Washington, D.C.. .
). In So Paulo, more than 85 per cent of at-risk households live in informal settlements, with more than half lacking access to appropriate sanitation and more than 30 per cent without access to paved roads (ibid.). In fact, health and sanitation problems within informal settlements exacerbate and create new risks. In Tanzania, for example, the lack of clean water and sanitation can lead to widespread outbreaks of waterborne diseases and malaria during flood episodes in informal settlements, thus creating further vulnerability (World Bank, 2011

World Bank. 2011,Dar es Salaam Case Study Overview, Climate Change, Disaster Risk and the Urban Poor: Cities Building Resilience for a Changing World. The World Bank, Washington, D.C.. .
The implementation of land-use and building regulations becomes a major challenge in such settings (UNISDR, 2011a

UNISDR. 2011a,Global Assessment Report on Disaster Risk Reduction: Revealing Risk, Redefining Development, Geneva, Switzerland: UNISDR.. .
; GAR 13 paperJohnson, 2011

GAR13 Reference Johnson, Cassidy. 2011,Creating an enabling environment for reducing disaster risk: Recent experience of regulatory frameworks for land, planning and building in low and middle-income countries, Background Paper prepared for the 2011 Global Assessment Report on Disaster Risk Reduction. Geneva, Switzerland: UNISDR..
Click here to view this GAR paper.
), particularly where high population density exacerbates existing risks. Under such conditions, what two innovative architects said about Caracas almost a decade ago may hold true for many urban settings today: “Considering ideal conditions is a waste of time […] The point is to avoid catastrophe” (Brillembourg and Klumpner, 2005

Brillembourg, Alfredo and Hubert Klumpner. 2005,Informal City, Prestel Publishing.. .
Concatenated urban risks
The growing complexity of interconnected urban systems in larger cities contributes to the structuring of the concatenated and potentially cascading disaster risks discussed in Chapter 10. These systems are directly shaped by the distinct features of individual cities and yet have common characteristics, notably their interconnectivity (Wamsler, 2014

Wamsler, Christine. 2014,Urban focus in climate change adaptation and risk reduction, Klimat Fokus, No. 12 (2014). Lund University.. .
). For example, the increasing dependence of water, sewerage, waste management and health systems on electricity supply has resulted in a shutdown of these critical services during power outages associated with hazard events such as the Akalla tunnel fire in Stockholm in 2002 or Hurricane Sandy in New York in 2012 (ibid.).
In urban centres, risk is amplified by the degree of interdependence of sectors, utilities and infrastructure, particularly in those cities that act as key nodes in the global economy and national markets (Airmic Technical, 2013

Airmic Technical. 2013,Supply Chain Failures: A study of the nature, causes and complexity of supply chain disruptions, A report by Dr. Alan Punter on behalf of Airmic - Sponsored by Allianz Global Corporate & Specialty & Lockton. London.. .
; OECD, 2009

OECD (Organisation for Economic Co-operation and Development). 2009,Privatisation in the 21st Century: Recent Experiences of OECD Countries Report on Good Practices, Paris.. .
). For example, in cities with little built-in redundancy, failures in the power grid quickly spill over into telecommunications and transportation, which in turn impact production, banking and other sectors.
In late 2012, Hurricane Sandy brought about such system failures at the very core of a major global economic hub. Operations in the Port of New York and New Jersey were interrupted, leading to a disruption of cargo services and, crucially, maritime first responders. This had extensive and prolonged impacts on both the Port and the emergency response sector. The New York Stock Exchange was forced to close for two consecutive days, the only time this has happened since a major winter storm in 1888, and more than 20,000 flights were cancelled. Internet traffic around the globe was also affected due to the role of New York as a major hub for data traffic (National Hurricane Center, 2013

National Hurricane Center. 2013,Tropical Cyclone Report: Hurricane Sandy, Authored by Eric S. Blake, Todd B. Kimberlain, Robert J. Berg, John P. Cangialosi and John L. Beven II. 12 February 2013.. .
; Smythe, 2013

Smythe, Tiffany C. 2013,Assessing the Impacts of Hurricane Sandy on the Port of New York and New Jersey’s Maritime Responders and Response Infrastructure, Quick Response Report No. 238: Final Report to the University of Colorado Natural Hazards Center Quick Response Grant Program (National Science Foundation grant CMMI1030670), 31 May 2013.. .
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