As global temperatures rise, thermal expansion of oceans and melting ice sheets are driving up sea levels worldwide. In many coastal areas, land subsidence—caused by groundwater extraction and rapid urbanization—further exacerbates flood risks. However, a new study reveals that in China, policy decisions on where and how to develop coastal land may have a more significant impact on future flooding than climate change itself.

The study, led by researchers from the Institute of Geographic Sciences and Natural Resources Research (IGSNRR) of the Chinese Academy of Sciences, was recently published in Nature Climate Change.

The researchers warn that policy uncertainties—specifically, whether cities expand into high-risk coastal zones or adopt protective land-use strategies—will be a decisive factor in determining how many millions of people and how much critical infrastructure could be affected by flooding by 2100.

"Coastal populations and economies are growing globally. Given the uncertainties surrounding climate change and global politics, it's not surprising that future development policies remain highly unpredictable," said Prof. WANG Yafei, associate professor at IGSNRR and lead author of the study. "Understanding how these policy uncertainties interact with land subsidence and sea-level rise to shape flood risk is a pressing scientific challenge."

For the first time, the researchers developed an integrated analytical framework that incorporates three key drivers of coastal flood risk: land-use policies (including urbanization, agricultural expansion, and ecosystem protection), climate factors (sea-level rise, storm surges, and tidal patterns), and land subsidence. By linking high-resolution land-use data with various policy scenarios and climate projections from the Intergovernmental Panel on Climate Change (IPCC), the method provides a novel approach to assessing how policy decisions can either amplify or mitigate future flood exposure.

Crucially, this integrated model enables scientists to distinguish between the physical extent of potential inundation and the social and political choices that determine which communities, industries, and infrastructure are most vulnerable.

The study identifies four primary hotspots of coastal vulnerability in China: the Pearl River Delta, Yangtze River Delta, Liaohe River Delta, and Bohai Bay. These regions are characterized by both low-lying terrain and dense urbanization, making them particularly susceptible to flood risks.

"Our findings show that the choices we make today regarding development, land management, and climate adaptation will define the resilience of China's coasts through 2100 and beyond," WANG emphasized. He also cautioned against overreliance on seawalls and levees, noting that such structures can create a "levee effect"—a false sense of security that encourages further development in high-risk areas, ultimately increasing long-term vulnerability.

Murray Scown, associate senior lecturer at the Lund University Centre for Sustainability Studies (LUCSUS) and a co-author of the study, highlighted actionable solutions for mitigating flood risks. "Governments and local authorities have a range of tools to protect coastal cities and communities. For instance, designing urban landscapes with parks that can safely absorb periodic flooding while serving as recreational spaces during dry periods. More broadly, spatial planning that restricts development in high-risk zones is critical. Additionally, reducing global carbon emissions is essential to slow accelerating sea-level rise—by beyond 2100, this could become the dominant flood risk factor not just in China, but worldwide."

This study was collaboratively conducted by researchers from China and Europe. Their findings can help identify which risk drivers are most critical for mitigation efforts, how these drivers interact, and where decision-making authority and resources for risk management should be directed, the researchers noted.