Objective In the context of the normalization of global extreme weather, resilient design has become the focus of urban construction and urban design disciplines. Through literature review, it can be found that storm-flood resilience and sponge city are the core issues in the construction of coastal resilient cities. However, at present, there is still a lack of research on the mapping between the 4R (robustness, redundancy, resourcefulness, and rapidity) resilience characteristics and spatial elements and specific measures in urban design, or the evaluation of the performance of specific resilience strategies under different scenarios. The conduction relationship between urban resilience theory and urban design practice needs to be further rationalized and refined. Based on the perspective of urban design, this research aims to explore the correspondence between urban spatial form and stormwater resilience indicator, and put forward a research framework suitable for resilience evaluation of coastal cities.

Methods The research uses literature research, empirical research, quantitative analysis and other methods. Based on literature induction and extraction and integration of 4R resilience characteristics, a comprehensive evaluation model with 24 indicators fallen into the four categories of robustness, redundancy, resourcefulness and rapidity is constructed. According to the four principles of typicality, international influence, resilience construction experience and multi-scenario difference, 9 typical coastal city samples at home and abroad are selected in a targeted and differentiated way for a global empirical research. They are the Lower Manhattan of New York City, the central area of Boston, the Silicon Valley area of Santa Clara, the central area of Copenhagen, the central area of Sydney, the central area of Singapore, the core area of Hong Kong Island, the Fushan Bay Business District of Qingdao, and the waterfront area of Zhuhai. Then, this research analyzes how each sample above improves its 4R resilience level through urban spatial form and functional layout.

Results According to the analysis results, Boston is the only sample city scoring above average in all the four categories, showing a high level of overall resilience. For other cities, New York and Sydney excel in redundancy and resourcefulness. The resourcefulness and rapidity of Qingdao and Singapore contribute the most to the overall resilience level. Hong Kong attaches the highest importance to resourcefulness; Copenhagen, Santa Clara and Zhuhai need to focus on their resilience strategies in terms of robustness and rapidity. The reasons leading to the aforesaid results are mainly summarized in the following three aspects. 1) Due to dense population and land shortage, city samples with high development intensity pay more attention to spatial redundancy and resource acquisition during disasters, and their urban core functional areas have achieved full coverage of public services and emergency service facilities to a large extent through encrypted road networks, mixed land use, vertical functional layout and other ways. At the same time, reasonable division of land parcels is also conducive to the construction of green belts and green corridors in urban areas. For example, cities such as Singapore and Boston are significantly higher than other cities of the same type in terms of rapidity indicators. 2) The coastal space of city samples with low development intensity is sufficient, which can withstand and dissolve the impact of stormwater through better shoreline protection and blue-green network. These city samples have the conditions to establish a generous coastal buffer zone, which can prevent coastal storm surge from attacking the urban core area in the first time. In addition, the clear separation of internal clusters through green belt can greatly enhance their retention and filtration of rain and flood. On the contrary, due to the large land scale and low degree of development and construction, city samples with low development intensity are typically featured by relatively poor spatial redundancy and relatively sparse distribution of emergency rescue facilities. 3) There is no significant correlation between the overall performance of 4R resilience and development intensity in coastal cities, and cities with different development intensity can enhance the overall resilience level by strengthening their own advantages or appropriately compensating for weaknesses. In city samples with high development intensity, priority should be given to improving the layout of redundant units and emergency resources, and the robustness and rapidity level should be improved by broadening the coastline and connecting the greenways. In city samples with low development intensity, road network should be properly encrypted and public service facilities should be evenly distributed to ensure better coverage of resource services in the context of ecological city construction.

Conclusion Through the empirical evaluation of typical coastal city samples, the guidance and control priorities and improvement strategies of coastal cities from the 4R evaluation dimensions are summarized. Coastal cities should consolidate coastal infrastructure combining resistance and buffering, strengthen three-dimensional and complex redundant functional units, build an integrated emergency rescue system spanning from coastal areas to hinterland, and improve the blue-green ecosystem by combining point, line and surface. In the future, China’s coastal cities should shore up the weakness of planning homogeneity, fully learn from excellent coastal urban construction cases at home and abroad, classify and implement policies through 4R resilience evaluation results, formulate a resilience strategy system for coastal cities in line with local environmental characteristics, and integrate such system into specific urban spatial form, functional layout and emergency management.