Sponge City Principles Adopted by Yanji City, China for Flood-Resilient Transit Systems

China’s Sponge City Program (SCP) represents a significant shift towards sustainable urban development in response to severe environmental challenges posed by rapid urbanization and climate change. This innovative program aims to transform urban water management by mimicking natural processes to absorb, store, and purify rainwater. By integrating natural blue (rivers, wetlands) and green (green roofs, rain gardens) spaces, sponge cities mitigate flood risks, improve water quality, and enhance urban resilience. The program's impact is substantial: as of 2019, it had invested around $60-90 million per city for initial projects, with total construction costs estimated at approximately EUR 1 trillion by 2030. These investments are expected to support a significant transformation, with an ambitious goal of equipping 80% of cities with sponge city infrastructure. The SCP not only addresses immediate flood and water management challenges but also contributes to increased urban biodiversity, cooler temperatures, and improved quality of life (3). Starting with pilot programs in 2015, the initiative has led to nearly 5,000 projects and the development of sponge city plans in 538 cities by 2018. This approach has inspired similar efforts in cities such as Berlin and Hamburg, emphasizing integrated flood management and water conservation. The Asian Development Bank has supported these projects, including the original pilot in Pingxiang (1). Germany's experience with green roofs and façades further illustrates the advantages of green infrastructure, with substantial progress in expanding green roof areas and setting a benchmark for other countries. By 2019, approximately two-thirds of German cities mandated green roofs in development plans, leading to a dramatic increase in green roof coverage to 120 million m² over the past decade (2).