By Bas Jonkman and Mathijs Van Ledden
One year ago Tuesday, Hurricane Sandy, perhaps the largest Atlantic storm ever, began its path of destruction in New York City. It ultimately killed almost 300 people across seven countries. In the United States alone, the fierce storm left an estimated $70 billion in damage in its wake, the second-costliest storm in U.S. history.
Substantial money and effort has now gone into rebuilding the areas most devastated by the storm. The truth is, however, that many other areas of the world, including in the United States, are just as vulnerable to intense flooding.
Existing flood protection in most countries is simply not fit for this purpose. Even in our native Netherlands, a world leader in flood management, roughly one-third of the defenses is sub-standard.
The combined impact of climate change, subsidence, urban growth and socio-economic change mean that average global flood losses could rise dramatically if no adequate risk reduction measures are implemented.
A new global agenda to enhance flood protection infrastructure is badly needed. This must be started now.
Having confronted water hazards for generations, the Dutch are eager to share their experience in planning and design of effective systems to reduce storm surge risk. We have learned how to protect the country against flooding and have developed a sophisticated system — a complex network of canals and pump stations to drain excess water.
Almost 3,800 km of flood defenses are in place to defend the country against major floods. The system includes earthen levees along rivers and sand dunes, coastal dikes and five major coastal dams and barriers along the coast.
For densely populated and strategically important areas, this strategy is generally more cost efficient than moving people, planning strategies or evacuation measures. As India's response to Cyclone Phailin recently demonstrated, however evacuation and early warning can also be effective in reducing risk to life
A combination of solutions will be needed to realize this agenda. These options include "hard" measures (engineering and building barriers and levees); "soft" options (strengthening existing natural features like dunes ); and also "hybrid" approaches (foreshores strengthened by vegetation for dikes).
One effective hard solution for protecting coastal metropolitan areas are storm surge barriers — as we have here in the Netherlands. However, the construction and maintenance costs are high — sometimes billions of dollars.
As the experience of the Netherlands shows, they can also take many years to plan and build. And there might be adverse effects for navigation and the environment.
Nonetheless, various cities, including New Orleans and St. Petersburg, have recently implemented this solution. Others, such as Shanghai and the Houston-Galveston area are studying this option.
The current proposals for New York City demonstrate a preference for more localized options, including flexible flood defenses for low-lying areas at waterfronts and protection measures to flood-proof subway and road tunnel systems. Softer solutions, including reinforcing wetlands in Jamaica Bay and dunes in front of coastal towns, are also being proposed
Natural solutions, such as dunes and berms, can often be implemented faster to implement and more adaptable to changing conditions than hard solutions, such as levees. However, there are still many uncertainties over the long-term safety of these soft solutions.
The solutions that New York City eventually chooses will be relevant for other flood-prone regions. This is not just for areas at risk in the United States, like the Houston- Galveston region and Sacramento, California, but regions in other parts of the world — especially growing megacities like Guangzhou, China, Ho Chi Minh City, Vietnam, and Bangkok, Thailand, where people face the challenging question of how to achieve sustainable flood protection.
Based on Dutch best practices, far more investment is needed in flood management globally to realize this agenda. With a national population of almost 16 million, the Dutch government already spends about 0.2 percent of its gross domestic product on managing a complex flood management system. Despite this investment, it is anticipated that costs could rise substantially due to aging infrastructure and future demands associated with sea level rises.
Other countries will also need to raise their own investment — some markedly so. A realistic target for flood adaptation is probably around 0.1 percent to 0.2 percent of the GDP at risk, significant but affordable.
Given the innovation and large sums of money required, part of this new agenda must be better distribution of roles and responsibilities between governments and the private sector. After the floods in Thailand and New York City, for example, the private sector has invested heavily in flood protection. Substantial floodwalls have now been built around industrial estates in Thailand, and measures have been implemented by companies in New York.
This is all positive. But governments must take care that local flood protection measures do not negatively affect other areas and put parties at risk. Therefore, there will always remain a key role for government to develop a long-term plan for flood management that sets a clear strategic framework and aligns all key stakeholders.
This combined agenda is as serious as it is pressing. It is an unfortunate reality, however, that societies seek to invest in adequate flood risk reduction only after large disasters. Given the scale of risks in coming decades, this attitude must now change for both human security and financial cost.
(Bas Jonkman is professor of hydraulic engineering at Delft University of Technology. Mathijs Van Ledden is director of flood risk reduction at Royal HaskoningDHV. Opinions are their own.)
- Nature & Environment
- Weather
- New York City
- flood protection
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