Adapting green roofs to climate change: Insights from case studies across four typical climates in China

As an effective measure for urban stormwater management, green roofs contribute to alleviating urban flood events and improving urban sustainability. To analyze the stormwater retention performance of green roofs and determine optimal designs under climate change conditions, this study used a hydrological model to evaluate their stormwater retention performance during 1970–2018 (49 years) and 2052–2100 (49 years) across four typical climates in China, including arid (Urumqi), semi-arid (Lanzhou), semi-humid (Beijing) and humid (Guangzhou) climates. Rainfall events in four cities were classified into non-extreme and extreme rainfall events using a percentile threshold method. The stormwater retention performance of green roofs was analyzed for long-term periods, non-extreme and extreme rainfall events. Results indicate that compared to 1970–2018, all four cities are projected to experience shortened antecedent dry periods, along with increased rainfall depth and frequency in 2052–2100. Under climate change conditions, the long-term stormwater retention rates (SRRs) of green roofs in the four cities are as follows: Urumqi (70.9–85.8 %) > Lanzhou (66.2–83.3 %) > Beijing (41.4–55.0 %) > Guangzhou (24.7–33.5 %). These findings demonstrate that green roofs can effectively retain rainfall under changing climate scenarios and perform better in arid and semi-arid climates than in semi-humid and humid climates. In future climate change projections, green roofs are effective at retaining non-extreme rainfall in all four climates, with SRRs exceeding 60 %. For extreme rainfall events, green roofs exhibit moderate SRRs (15.2–42.6 %) in arid and semi-arid climates but are less effective in semi-humid and humid climates (SRRs: 1.8–13.3 %). To achieve greater SRRs in the future, substrates with higher stormwater retention capacity are recommended for green roofs in arid, semi-arid and semi-humid climates, while high water-using plants and substrates with lower stormwater retention capacity are more suitable for humid climates. This study provides a comprehensive assessment of stormwater retention performance and offers a scientific basis for optimizing green roofs configurations across diverse climates under climate change conditions.