In 2005, Hurricane Katrina struck the Mississippi delta in the state of Louisiana. The severe flooding that followed led to the death of 1,800 people. Over a million were displaced and the direct economic losses reached more than US$100 billion. One of the worst natural disasters in US history was made much worse by long-term destruction of the delta wetlands, which would otherwise have absorbed much of the seawater that surged into the city of New Orleans.
In response to the disaster, Congress authorised a $14 billion reconstruction of the New Orleans flood defences, including a levee system strong enough to withstand once-in-a-century floods.
But in May 2018, just 11 months after those levees were completed, the US Army Corps of Engineers warned that rising sea levels and subsidence in the soft ground meant they may only last for another four years. It later called for an additional $3.2 billion to further reinforce the levees.
While acknowledging the importance of this work, some local environmental groups have argued that the levees will remain at risk regardless of their height. They cannot be the sole solution, they say.
Research is increasingly showing the promise of another approach: restoring wetlands to make coastal areas more robust and resilient to flooding. As we will see, China in particular could benefit greatly from this approach.
While climate change has seen hurricanes in the North Atlantic intensify, things are even more worrying on the other side of the world. China is especially vulnerable to climate change its sea levels have risen by more than the global average over the last 30 years, and typhoons that reach land have become stronger since the mid-1990s. China’s economic activity and populations are also concentrated on its coast, increasing the damage caused by storms. In 2018, Typhoon Mangkhut affected three million people across southern China, with 1.6 million evacuated, over 1,200 buildings destroyed, and 1.7 million hectares of crops damaged. Up to $120 billion of damage may have been caused across Asia as a whole.
In the wake of Mangkhut, experts warned that China would see more frequent and more powerful typhoons making landfall. It was estimated that 2020 would see 25-28 tropical cyclones form in the western Pacific and South China Sea, with six to eight making landfall in China. In August, three typhoons reached mainland China, with Zhejiang, Fujian and Guangdong provinces suffering damage worth 12.44 billion yuan (US$1.8 billion).
Since antiquity, those who live and work by the coast in China have built flood defences, and today levees and other coastal protections are key to disaster prevention efforts. But as experience in the US has shown, artificial defences have only limited effectiveness and require expensive annual repairs and maintenance.
Research shows that from the 1950s to the 2000s, China lost 53% of its temperate coastal ecosystems, 73% of its mangrove forests, and 80% of its coral reefs, mainly because of huge levels of development and land reclamation. As such, the country’s coastline has lost much of its capacity to resist increasingly intense storms.
But it is not yet too late. There is an ever-clearer awareness of the value of the ecological services provided by China’s coastal wetlands, and protection and restoration is now on the agenda for policymakers. In April 2017, President Xi said mangrove forests must be safeguarded while inspecting some in Guangxi. In July 2018, the State Council published a notice on better protection of coastal wetlands and tougher regulation of land reclamation projects. In June of this year, a 15-year plan for protecting and restoring key ecosystems was published future work will focus on saving and regenerating coastal vegetation such as mangrove forests, seagrass meadows and coral reefs. Then, in August, the Ministry of Natural Resources and the State Forestry Administration published a detailed 2020-2025 plan for protecting and restoring mangrove forests.
The ministry’s National Marine Hazard Mitigation Service is leading development of a system to assess and categorise the protection offered by coastal wetlands. Trial results indicate that mangrove forests with a width of 150 metres can reduce the height of a storm surge by 80%, while a belt of salt marsh vegetation 30 metres wide can reduce wave energy by 70%, and a 100-metre-wide grassy marsh reduces their energy by 90% proving how effective these wetlands are as barriers against the sea. In response to these findings, the ministry has led the drafting and release of a series of standards for the surveying, assessment, restoration and management of coastal ecosystems. While these standards are not binding, they are a positive step.
China Dialogue Trust