Can flood resilience of green-grey-blue system cope with future uncertainty?

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Urban flooding is becoming a great global concern due to growing cities, while climate change and urbanization may pose daunting challenges to both environment and humans. The integrated green-grey-blue (IGGB) system has gained interests worldwide to mitigate flood issues, however, how IGGB system acts in urban flood resilience and whether it can address future uncertainties have not been fully understood. In this study, a new framework, which combined an evaluation index system and coupling model, was constructed to quantify urban flood resilience (FR) and its responses to future uncertainties. The results showed that higher FR upstream than downstream; however, upstream FR declined approximately twice as much as downstream when faced with climate change and urbanization. Generally, climate change appeared to have a greater impact on urban flood resilience than urbanization, resulting to 3.20%-4.28% and 2.08%-4.09% FR reduction, respectively. The IGGB system could greatly improve robustness against future uncertainty, due to the fact that the IGGB without low impact development facilities (LIDs) was about 2 times in FR decline compared with IGGB with LIDs. The increase of LIDs proportion could diminish the impact of climate change, which shifted the dominant factor affecting FR from the interaction between urbanization and climate change to urbanization. Notably, a threshold of 13% construction land increase was quantified, beyond which negative effects of rainfall become dominant again. The results could guide IGGB design and urban flooding management in other similar regions.