Impacts of climate change and urbanization on soil moisture dynamics have reduced regional flood resilience

• Climate change and urbanization have reduced soil infiltration and water retention capacity. • Compact urban morphology as a key strategy to mitigate soil moisture loss and enhance hydrological resilience. • Urban cores and boundaries, river banks, coastal areas, and key natural points are spatial clusters of flood risk. • Integrating compact cities, ecological buffer areas, and wetland networks can enhance flood adaptability. • The soil moisture dynamics as an empirical tool for assessing flood resilience. Climate change, by altering precipitation and potential evapotranspiration, and urbanization, through reducing soil pore and infiltration capacity, both undermine soil water retention and increase flood risks. However, little is known about the combined impact of these factors on soil moisture dynamics. We assessed soil moisture dynamics in the Guangdong-Hong Kong-Macao Greater Bay Area from 1985 to 2022. A flood resilience map was developed using a robustness index based on soil moisture. The findings indicate that urbanization has significantly reduced soil moisture in urban areas ( β = −0.11). Regional soil moisture showed a slight increasing trend, and the estimated coefficients for precipitation and potential evapotranspiration were 0.33 and −0.37, respectively. Urbanization primarily reduced soil moisture in urban areas, while climate change increased soil moisture in regional and natural areas. Meanwhile, notable fluctuations were observed across urban cores, urban boundaries, and coastal areas, indicating the system’s low robustness. The flood resilience risk space exhibited a three-tiered structure, comprising high-risk cores, medium-risk belts, and low-risk points. The three-tier spatial planning framework is proposed to enhance flood resilience: (1) managing compact urban form with a compactness index range of 1.60–1.65, (2) developing a 6.5 km resilient sponge network within the urban boundary where the built-up area fraction remains below 41%, and (3) restoring permeable substrates along coastal areas. This framework evaluates regional resilience through the spatiotemporal dynamics of soil moisture, assessing regional robustness and mapping flood risk for high-density urban agglomerations facing extreme climate events.