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Future flood losses in major coastal cities


Flood exposure is increasing in coastal cities1,2 owing to growing populations and assets, the changing climate3, and subsidence4,5,6. Here we provide a quantification of present and future flood losses in the 136 largest coastal cities. Using a new database of urban protection and different assumptions on adaptation, we account for existing and future flood defences. Average global flood losses in 2005 are estimated to be approximately US$6 billion per year, increasing to US$52 billion by 2050 with projected socio-economic change alone. With climate change and subsidence, present protection will need to be upgraded to avoid unacceptable losses of US$1 trillion or more per year. Even if adaptation investments maintain constant flood probability, subsidence and sea-level rise will increase global flood losses to US$60–63 billion per year in 2050. To maintain present flood risk, adaptation will need to reduce flood probabilities below present values. In this case, the magnitude of losses when floods do occur would increase, often by more than 50%, making it critical to also prepare for larger disasters than we experience today. The analysis identifies the cities that seem most vulnerable to these trends, that is, where the largest increase in losses can be expected.

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Figure 1: The 20 cities where the relative risk is larger in 2005, that is, where the ratio of AAL with respect to local GDP is the largest.
Figure 2: The 20 cities where AAL increase most (in relative terms in 2050 compared with 2005) in the case of optimistic sea-level rise, if adaptation only maintains present defence standards or flood probability (PD).

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These are early results from an ongoing OECD research project. The authors acknowledge support from the OECD for this research and support from J. Chateau to provide the socio-economic scenario data from the OECD’s ENV-Linkages model. C.G. acknowledges support from the AVOID project. The views shared in this article represent those of the authors and are not intended to represent the views of the OECD or of its Member countries, or the view of World Bank, its executive directors, or the countries they represent.

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The four authors designed the study, interpreted results and authored the paper. S.H. developed and ran the models. R.N. and C.G. provided expert input on depth–damage curves and coastal protection.

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Correspondence to Stephane Hallegatte.

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The authors declare no competing financial interests.

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Hallegatte, S., Green, C., Nicholls, R. et al. Future flood losses in major coastal cities. Nature Clim Change 3, 802–806 (2013).

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