IDSS Presents: Present and Future Flood Risk in Large Coastal Cities, and Implications for Risk Management Policies

Flooding in Ho Chi Minh City

BBC World Service


Stephane Hallegatte
World Bank


February 14, 2014 Cancelled due to weather


RAND Corporation
1776 Main Street
Santa Monica, CA

About the Program

Flood exposure is increasing in coastal cities due to growing populations and assets, the changing climate, and subsidence. The presentation will 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, the assessment accounts for existing and future flood defences.

Average global flood losses 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, current protection will need to be upgraded to avoid unacceptable losses. Even if adaptation investments maintain flood probability, subsidence and sea level rise will increase mean annual losses by between 15 and 22% in 2050 on top of the increase due to socio-economic changes. The analysis identifies the cities that appear most vulnerable to these trends, i.e., where the largest increase in losses can be expected.

To maintain flood risk, adaptation will need to reduce flood probabilities below current 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 presentation will conclude with a discussion on the estimation of indirect losses due to such large scale floods. Modeling and statistical analyses suggest that large-scale disasters have consequences that extend beyond loss of lives and assets. There are also large output losses, loss of jobs, and a long recovery period that affect welfare for a longer period of time. The introduction of policies to reduce these indirect losses and shorten the recovery period is a potentially interesting complement to classical flood management measures that aim at reducing direct flood losses.

About the Speaker

Stéphane Hallegatte is senior economist with the World Bank, in the office of the chief economist of the Sustainable Development Network. His work includes green growth and climate change mitigation strategies, urban economics, and climate change adaptation and disaster risk management. He is lead author of the IPCC for its fifth assessment report. He also co-led the World Bank report “Inclusive Green Growth” in 2012, and is a core writing team member for the 2014 World Development Report "Managing Risks for Development." Hallegatte holds an engineering degree from the Ecole Polytechnique and a PhD in economics from the Ecole des Hautes Etudes en Sciences Sociales in Paris.

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