Abstract Blue‐green roofs (BGRs), compared to traditional green roofs, can provide enhanced water storage capacity for stormwater management and drought mitigation. However, the potential of utilizing stored water for external purposes, such as toilet flushing and lawn irrigation, remains underexplored. This study developed a daily time‐step hydrological model based on the water balance equation to simulate the runoff reduction ratio, water supply reliability, and irrigation time fraction of BGRs with water supply functions. Using summer rainfall and evapotranspiration (ET) data (1980–2013) from six climatically different cities based on Köppen climate zone classification in the United States (Atlanta, Flagstaff, Billings) and China (Guangzhou, Jinan, Lanzhou), the study revealed that: (a) BGRs with external water supply significantly improve runoff control and water supply benefits but increase irrigation demands, particularly in arid regions; (b) increasing storage layer capacity enhances BGRs' performance, but benefits diminish beyond 50 mm; (c) adaptive water supply strategies based on climate variations can improve both flood control benefit and irrigation reliability for BGRs; and (d) water deficits can be avoided in high‐rainfall or low‐ET regions. These findings provide valuable insights for optimizing BGR design and management in diverse climatic conditions.
Plain Language Summary Blue‐green roofs (BGRs) offer enhanced water storage capacity compared to traditional green roofs, aiding stormwater management and drought mitigation. This study developed a daily time‐step hydrological model to simulate runoff reduction performance, water supply reliability, and irrigation demand of BGRs with water supply functions. Using summer rainfall and evapotranspiration (ET) data (1980–2013) from six cities in the U.S. and China, the study found that: (a) BGRs with external water supply greatly increase runoff reduction and water supply benefits, but need higher irrigation demands; (b) increase in storage layer capacity enhances system's performance, but benefits decrease beyond 50 mm; (c) climate‐adaptive water supply strategies can help increase runoff control benefit and satisfy irrigation demand for BGRs; and (d) water supply and demand balance is achievable in areas with high rainfall or low ET. These findings can help proper BGR design and management in areas with different climate conditions.
Key Points A daily hydrological model was developed for water‐supply enabled blue‐green roofs Blue‐green roofs' external water supply potential was explored for non‐potable applications Hydrologic performance for blue‐green roofs were assessed across six cities