Resilient Economies Strategies for Sinking Cities and Flood Risks 2025

To identify the most suitable and sustainable strategies, each city must assess its unique context, including geographic characteristics, underlying subsidence drivers, development and climate risk factors, fiscal capacity and stakeholder alignment. Careful evaluation of each solution’s benefits, drawbacks, and potential combinations can enable cities to implement context-specific, feasible, and sustainable approaches. In assessing the appropriate solutions, stakeholders are also encouraged to consider unintended consequences, including the impact of water and land management on cities, economies and communities upstream and downstream from their location. Peer-to-peer exchange and evidence-based learning are critical. By drawing on tried-and-tested solutions, cities and their partners can better understand the benefits, limitations and unintended consequences of solutions, such as: –Retention infrastructure can support flood control in subsiding areas, but may involve high capital costs, environmental disruption and community displacement. –Sea walls can protect against tidal floods and storm surges, but can cause land erosion and beach loss by blocking the natural movement of sand, potentially undermining their own effectiveness.137 –Dams can potentially disrupt the sediment flow, leading to erosion below the dam. A lack of sediment replenishment in delta areas can also cause the loss of wetlands.138 –Underground discharge channels can reduce surface flooding, but can require significant investment and technical requirements for large- scale impact.139 –Green roofs can enhance water absorption and reduce runoff, though they require upfront investment and regular maintenance compared to standard roofs. However, long-term savings can offset costs.140 Engaging public-private sector experts who understand the interconnections and long-term impacts of these solutions is key preventing current and future risks and costs of subsidence and compounding impacts. Sinking challenges also provide opportunities to harness technologies such as digital twins, satellite, artificial intelligence (AI) or machine learning, and the internet of things (IoT) to obtain reliable, up-to-date data and real-time data to inform decision-making. Stakeholders are encouraged to consider unintended consequences, including the impact of local water and land management on cities, economies and communities. Resilient Economies: Strategies for Sinking Cities and Flood Risks 29