Greening the gray

This year has seen many severe weather and climate disasters, including record-breaking heat and drought in North America, and floods and heavy rains in central Europe and China's Henan province, leading to significant losses of lives and properties. However, these are by no means isolated natural disasters, as extreme weather events are happening with increasing frequency as the global temperature rises.

According to the latest report of the Intergovernmental Panel on Climate Change, Climate Change 2021－The Physical Science Basis, the average global temperature is on course to rise 1.5 C above pre-industrial levels in the following decade, earlier than expected. This means there will be more dramatic climate fluctuations and more extreme weather events. Coastal areas, in particular, will face multiple threats such as rising sea levels, intensified typhoons and a sharp increase in the risk of coastal erosion and floods.

China has the longest coastline in the western Pacific Ocean and has suffered from natural marine disasters throughout its history. According to the China Meteorological Bulletin, the accumulated direct losses from typhoons in China were 665.18 billion yuan ($102.9 billion) from 2011 to 2020, equivalent to the total output of the 54 least developed economies in the world. Meanwhile, China's coastal areas are the most highly populated, economically active and densely built-up areas in the country. Covering 13 percent of the land area, the 11 coastal provinces involved in our studies are home to 43 percent of the Chinese population and generate 53 percent of China's GDP, attracting 45 percent of the total fixed-asset investment. Against the backdrop of climate change, the rate at which the sea level is rising in China's coastal areas is higher than the global average over the same period, which will provide a higher water base for gale-force winds and waves, significantly increasing the frequency and intensity of storm surges, rogue waves and other major marine risks. If coastal infrastructure such as seawalls are not strengthened in time, the losses suffered by coastal areas from typhoons and storm surges will escalate.

As an essential part of the coastal disaster prevention and mitigation system, seawalls serve as a means of protection against floods, waterlogging, high tides, storm surges and typhoons, ensuring the safety of people's lives and properties and promoting sustainable economic development. However, in China, about 4,000 kilometers of coastline are still not adequately protected by seawalls from tides, and most of the existing seawalls have low construction standards and poorly maintained facilities. Moreover, global warming has made the frequency and intensity of marine disasters less predictable, further exacerbating the limited protection capacity in the coastal areas. In addition, since the design of disaster prevention and reduction infrastructure in China used to take little account of eco-friendly concerns and favor gray infrastructure (e.g.concrete dykes), the ecological service capacity and ecosystem integrity in the coastal areas have been degraded.

Over the past decades, many countries, including the Netherlands, Mexico, Malaysia and China, have been actively piloting climate-resilient coastal designs. Among them, shoreline projects that integrate gray and green (shoreland vegetation) infrastructures stand out. The combination of gray and green seawalls has proven to be effective not only in protecting against typhoons and storm surges, but also in reducing erosion and ground subsidence, minimizing the retreat of natural shorelines, and preventing the loss of coastal infrastructure such as land, houses and roads. Green-gray seawalls serve as an effective approach to address the deep uncertainty of future climate risks and bridge the gap between the growing demands for flood protection and the lagging seawall construction along the shoreline. In terms of economic benefits, restoring the ecosystem around seawalls can boost the coastal and marine tourism industry, and raise the value of property in beachfront communities. In terms of social and environmental benefits, green infrastructure such as mangroves have multiple ecological functions, such as carbon sequestration, oxygen generation, air and water pollutant removal, and biodiversity enhancement of the coastal area.

The National Seawall Construction Program issued in 2017 put forward requirements for implementing the green development concept in future infrastructure construction plans. However, many pilot projects, such as Chongming Island in Shanghai and Hongshahuan in Fangchenggang, Guangxi Zhuang autonomous region, have shown mixed results. Despite having higher climate resilience, the integrated green and gray seawalls cost 50 percent to 100 percent more than traditional ones that are purely gray. Thus, the conventional infrastructure financing model that entirely depends on government funding is no longer applicable and sustainable.

Globally, an enabling environment for the construction of climate-resilient infrastructure is already in place. More than 30 world leaders, including Chinese Vice-Premier Han Zheng, have expressed their enhanced ambitions to upgrade climate-resilient infrastructure and strong support for expanding funding sources for adaptation and resilience at the Climate Adaptation Summit in early 2021. Meanwhile, China has created favorable conditions for comprehensively and systematically evaluating the cost and benefit of green and gray integrated infrastructure by implementing the Gross Ecosystem Product national pilot program and other technological explorations since 2004. These achievements also pave the way to internalize the currently uncompensated social and environmental impacts of climate-resilient infrastructure. Local governments must capitalize on establishing an enabling financial, technological, and political environment and seize the opportunity to fully mobilize private investment to plan and construct climate-resilient infrastructure, securing China's coastal areas to develop in a safe, inclusive and sustainable way.

Lu Lu is a research analyst of the Sustainable Cities Program at the World Resources Institute (China).Helen Ding is an environmental economist of the Economics Center at the World Resources Institute (United States). The authors contributed this article to China Watch, a think tank powered by China Daily. The views do not necessarily reflect those of China Daily.