Managing stormwater on urban surfaces with blue-green infrastructure (BGI) is being increasingly adopted as an alternative to conventional pipe-based stormwater management in cities. BGI combats water problems and provides multiple benefits for cities, including improved livability and enhanced biodiversity. The paper examines six municipality-led pilot projects from Beijing and Copenhagen, through a review of documents, site observations and interviews with project managers. Beijing’s projects attempt to divert from a pipe-based approach but are dominated by less BGI-based solutions; they could benefit from more integration of multiple benefits with stormwater management. Copenhagen’s projects combine stormwater management with amenity improvement, but lack focus on stormwater utilization. Reviewed municipality-led pilot projects are shown to play an important role in both testing new solutions and upscaling them in the process of developing more sustainable cities. Key lessons are extracted and a simple guideline synthesized. This guideline suggests necessary considerations for a holistic solution that combines stormwater management and urban space improvements. Key lessons for sustainable solutions include defining a clear water technique priority, targeting both small and big rain events, strengthening ‘vertical design’ and providing multiple benefits. An integrated stormwater management and landscape design process is a prerequisite to the meaningful implementation of these solutions. Research and documentation integrated with pilot projects will help upscale the practice at city scale.

To solve the problems of increasing local flooding, water shortage, and water pollution caused by the traditional model of urban development, the Chinese government proposed a new model of urban development—the Sponge City. In Beijing, the capital of China, research on storm water management in urban areas has been carried out since 1989 and has put forward the concept of urban storm water harvesting and flood control. The further research and demonstration application started in 2000. So far, a series of policies and technology standards on storm water management have been formulated, which promote the application of technologies on comprehensive urban storm water harvesting and flood control. A significant number of storm water harvesting and flood control projects have been built in Beijing, which are now playing important roles in runoff reduction, local flood control, non-point source pollution reduction, and storm water utilization. However, it does not solve the above problem completely. Storm water management and flood control needs to be further strengthened. The “Sponge City” is based on natural and ecological laws, which allows storm water to be managed with natural infiltration, natural retention and detention, and natural cleaning facilities. Through in-depth analysis of the connotation, characteristics, and construction path of “Sponge City”, this paper summarizes the status quo of urban rainwater flooding, flood control technology development and application, and Beijing policy and engineering to introduce the overall ideas and methods of Sponge City construction. All the above will provide a reference for cities with similar problems in the construction of sponge cities.

Antecedent soil moisture determines how much storage remains in bioretention media before rainfall, but its relationship with runoff control is poorly quantified. Three wet seasons of monitoring were analyzed for two field-scale bioretention systems with contrasting media depths, runoff loading, and drainage boundaries. For each event, antecedent available storage was calculated from the initial soil moisture profile relative to field capacity and, separately, to the 95th percentile of peak water content at each depth. Event-activated storage was defined as the greatest synchronous increase in water stored across the monitored profile following rainfall onset. Both storage metrics were expressed as equivalent rainfall depths over the contributing roof area. Runoff volume reduction ranged from 62.3% to 100% in BR1 and from 43.3% to 100% in BR2. Median event-activated storage over the media area was 4.9 mm in BR1 and 19.1 mm in BR2. However, after conversion to the contributing roof area, median antecedent storage was larger in BR1 than in BR2 under both the field capacity reference (3.8 versus 0.6 mm) and the high water reference (11.0 versus 5.0 mm). Greater antecedent storage was associated with a lower probability of drainage activation in both systems and greater runoff volume reduction in BR1. In BR2, greater event-activated storage was associated with lower runoff volume reduction, indicating that stronger within-event media wetting did not necessarily correspond to greater facility-scale runoff retention. Dynamic storage should therefore be interpreted in relation to hydraulic loading, media configuration, and drainage pathways.