Yangtze Delta China - Sharing Resilience and Innovation
“I am sure that if the river was like it is today, smoothened with concrete flood walls, I would have drowned.”
In providing high spatial resolution land subsidence velocities for the 48 largest coastal cities worldwide which represent 20% of the global urban population, Tay et al. (2022) show that delta cities experiencing the fastest subsidence are concentrated in Asia. In China, urban floods have become a major concern due to climate change and rapid urbanization on deltas. Major cities are affected e.g., Beijing (2012), Guangzhou (2014, 2015, 2020), Shenzhen (2014, 2020), Ningbo (2013) and Wuhan (2016, 2020).
Urban flooding, Yinzhou district, Ningbo. Typhoon Fitow, October 2013 (image: Faith Chan)
Conventional urban flood management often involves building pipes or drains to carry away water as swiftly as possible or reinforcing riverbanks with concrete to ensure they do not overflow. But a sponge city does the opposite, soaking up rainfall and slowing down surface run-off. Wong (2021) describes how it does this: firstly, at source, where like a sponge with myriad holes, a city holds water through multiple small ponds. Second, instead of funneling water away quickly in straight lines, meandering rivers with vegetated wetlands slow water down. This has the added benefit of creating green spaces, parks and wildlife habitats, with vegetation purifying run-off by absorbing toxins and nutrients. Finally, at the coast, managed retreat and avoidance of construction allow water to exit easily to the sea. Delta cities on the Pearl and Yangtze deltas have embraced the concept, much of which is influenced by traditional farming techniques such as storing rainwater in ponds for crops:"Nobody would drown, not even in the monsoon season. We just lived with the water. We adapted to the water when the floods came" (Wong, 2021). Digital platforms are used for flood alerts, public education, and community-driven monitoring and maintenance. This participatory locally led approach fosters shared responsibility for water management.
Ningbo Sponge City eco-corridor (image: Sitong Liu).
What would a UN Convention on River Deltas do?
Facilitate inter-delta knowledge sharing, empowering urban-based delta communities to learn from successful schemes elsewhere; it would also help mobilize resources for these Nature-based Solutions and improve the policy coherence required for wider adoption of these initiatives on highly populated flood-prone delta landscapes.
Contributed by: Faith Ka Shun Chan, University of Nottingham Ningbo, China
