e! Science News 19 Aug 13;
Climate change combined with rapid population increases, economic growth and land subsidence could lead to a more than nine-fold increase in the global risk of floods in large port cities between now and 2050. "Future Flood Losses in Major Coastal Cities," published in Nature Climate Change, is part of an ongoing project by the Organisation for Economic Co-operation and Development (OECD) to explore the policy implications of flood risks due to climate change and economic development. This study builds on past OECD work which ranked global port cities on the basis of current and future exposure, where exposure is the maximum number of people or assets that could be affected by a flood.
The authors estimate present and future flood losses -- or the global cost of flooding -- in 136 of the world's largest coastal cities, taking into account existing coastal protections. Average global flood losses in 2005, estimated at about US$6 billion per year, could increase to US$52 billion by 2050 with projected socio-economic change alone.
The cities ranked most 'at risk' today, as measured by annual average losses due to floods, span developed and developing countries: Guangzhou, Miami, New York, New Orleans, Mumbai, Nagoya, Tampa-St. Petersburg, Boston, Shenzen, Osaka-Kobe, and Vancouver. The countries at greatest risk from coastal city flooding include the United States and China. Due to their high wealth and low protection level, three American cities (Miami, New York City and New Orleans) are responsible for 31 per cent of the losses across the 136 cities. Adding Guangzhou, the four top cities explain 43 per cent of global losses as of 2005.
Total dollar cost is one way to assess risk. Another is to look at annual losses as a percentage of a city's wealth, a proxy for local vulnerability. Using this measure, Guangzhou, China; Guayaquil, Ecuador; Ho Chi Minh City, Vietnam; and Abidjan, Ivory Coast are among the most vulnerable.
To estimate the impact of future climate change the study assumes that mean sea-level, including contributions from melting ice sheets, will rise 0.2-0.4 meters by 2050. In addition, about a quarter of the 136 cities are in deltas and exposed to local subsidence and local sea-level change, especially where groundwater extraction accelerate natural processes.
An important finding of this study is that, because flood defences have been designed for past conditions, even a moderate rise in sea-level would lead to soaring losses in the absence of adaptation. Inaction is not an option as it could lead to losses in excess of $US 1 trillion. Therefore, coastal cities will have to improve their flood management, including better defences, at a cost estimated around US$50 billion per year for the 136 cities.
Robert Nicholls, Professor of Coastal Engineering at the University of Southampton and co-author of the study, says: "This work shows that flood risk is rising in coastal cities globally due to a range of factors, including sea-level rise. Hence there is a pressing need to start planning how to manage flood risk now."
Even with better protection, the magnitude of losses will increase, often by more than 50 per cent, when a flood does occur. According to Dr Stephane Hallegatte, from the World Bank and lead author of the study: "There is a limit to what can be achieved with hard protection: populations and assets will remain vulnerable to defence failures or to exceptional events that exceed the protection design." To help cities deal with disasters when they do hit, policy makers should consider early warning systems, evacuation planning, more resilient infrastructure and financial support to rebuild economies.
The report also notes that large increases in port city flood risk may occur in locations that are not vulnerable today, catching citizens and governments' off-guard. The five cities with the largest estimated increase in flood risk in 2050 are Alexandria, Egypt; Barranquilla, Colombia; Naples, Italy; Sapporo, Japan; and Santo Domingo, Dominican Republic.
Source: University of Southampton
Coastal Flooding Damage: $1 Trillion a Year by 2050
Tia Ghose LiveScience.com Yahoo News 18 Aug 13;
Coastal flooding in cities around the world could cause damage totaling $1 trillion annually by the year 2050 if no mitigating steps are taken, new research suggests.
Almost all cities facing the worst damage are in Asia and North America, the study showed. Three American cities — New York, New Orleans and Miami — are at particularly high risk of damage, according to the study, published today (Aug. 18) in the journal Nature Climate Change.
"If we did nothing about the risk, the flood damages in coastal cities would grow to huge amounts. So that's really not an option," said study co-author Robert Nicholls, a coastal engineering professor at the University of Southampton in England.
Damaging storms
Climate change models generally predict that storms will grow more frequent and fierce over the next several decades. We may already be seeing its impact: Many scientists believe that climate change worsened the toll of Hurricane Sandy. [How Weird!: 7 Rare Weather Events]
After Hurricane Katrina ravaged the Gulf Coast in 2005, Nicholls and his colleagues realized that scientists had little idea which cities around the world were most vulnerable to flooding.
So the team compiled data on 136 coastal cities with more than 1 million residents, looking at the elevation of the cities, the population distribution and the types of flood protection they had, such as levees or storm-surge barriers.
They then combined that data with forecasts of sea level rise, ground sinking due to groundwater depletion, as well as population growth projections and economic forecasts of gross domestic product (GDP). From there, they used the depth of water flooding a city to estimate the cost of the damage.
Two vulnerable continents
The researchers found that in both their best- and worst-case projections of sea level rise, the yearly global cost reached higher than $1 trillion. The most vulnerable city was Guangzhou, China, followed by Mumbai and Kolkata in India, Guayaquil, Ecuador and Shenzen, China. Almost all cities at the highest risk of flooding damage were in North America or Asia. [See The 20 Cities Most Vulnerable to Flooding]
If cities take steps to prevent damage — by increasing the height of levees, erecting storm surge barriers, making buildings flood-resistant or converting flood-prone, low-lying areas to parks or football fields — the cost of the damage could be brought down to about $50 billion annually.
It would be cheaper and more sensible to make these changes before Katrina-like storm surges become the norm, Nicholls said.
"The bottom line is it shows that flood risk is rising today — it's happening" Nicholls told LiveScience. "All these cities need to be preparing for that."
Full study in Nature Climate Change
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