Assessing Climate Change Impacts, Sea Level Rise and Storm Surge Risk in Port Cities: A Case Study on Copenhagen.

OECD Environment Working Paper No. 3
ENV/WKP(2008)2

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by Stéphane Hallegatte (1.2) ,Nicola Patmore (3), Olivier Mestre (2), Patrice Dumas (1), Jan Corfee Morlot (4), Celine Herweijer (3), Robert Muir Wood (3)
 
KEY MESSAGES

1/ Copenhagen, thanks to its location, is not highly vulnerable to storm surges and coastal floods. Man-made defences, however, are necessary: without them, the economic losses caused by the current 10 yr storm surge event, i.e. the surge that has a 1-out-of-10 chance of occurring every year, would reach EUR 2.5 billion.

2/ With current man-made defences (i.e., dikes and sea walls), most of the city is protected against all possible storm surges. An exception is the south western part of the agglomeration (including the stretch in Hvidovre), which is only protected against the 120-yr event.

3/ Without man-made defences, sea level rise would increase coastal flood risks in a significant manner. For instance, 50 cm of sea level rise would increase by 55% the losses caused by the 120-yr event, from EUR 3 to 5 billion.

4/ Current man-made defences are able to face significant sea level rise, but upgrades will be needed in a few decades in some important locations, including the harbour and the city historical centre. Experiences in other cities show that these upgrades need to be anticipated well in advance, within a comprehensive climate-change adaptation plan.

5/ Even with adequate defences, sea level rise will increase flood exposure, magnifying the consequences of any defence failure. This increase in exposure will make it even more necessary to carefully maintain the defences and to create effective disaster emergency and recovery plans.

6/ Many world cities, especially in developing countries, do not have such comprehensive flood defences, making them highly vulnerable to coastal floods and sea level rise. In these locations, losses will reach unbearable levels in absence of a strong change in risk management practices and in flood defence standards.

7/ Adaptation and upgrades in flood defences are the most efficient tools to reduce sea level rise losses over the short and medium terms. Over the long term, however, only mitigation can limit sea level rise to levels that are manageable with dikes and sea walls.

Contact Information:
OECD Project leader: Jan Corfee-Morlot, jan.corfee-morlot@oecd.org.
Lead author: Stéphane Hallegatte, hallegatte@centre-cired.fr.

Full Study

More information about the work on cities: www.oecd.org/env/cc

(1) Centre International de Recherche sur l’Environnement et le Développement.
(2) Ecole Nationale de la Météorologie, Météo France, Paris, France.
(3) Risk Management Solutions Limited, London, UK.
(4) Organisation for Economic Co operation and Development, Paris, France.