Exploring urban expansion pattern associations with flood Vulnerability: Spatial heterogeneity in multidimensional linkages across China's Min Delta urban agglomeration

Coastal cities globally face escalating flood events under climate change and rapid urbanization, threatening sustainable development. While urbanization amplifies flood vulnerability (FV), inconsistent relationships between urban expansion patterns (UEPs) and FV persist. To address this gap, this study resolves UEP-multidimensional FV relationships while examining inter-city developmental disparities through an integrated assessment of China's Min Delta Urban Agglomeration (1990-2020), combining Landscape Expansion Index with entropy-weighted multidimensional FV metrics validated by Geographically Weighted Regression and correlation comparisons. Results reveal regional expansion peaked during 2000-2010 before declining, except Zhangzhou, where delayed urbanization sustained growth. Edge expansion (EE) dominated, infilling expansion (IE) intensified, and leapfrog expansion (LE) remained minimal. Due to persistent urban expansion, natural vulnerability (NV) increased inland-to-coastal and intensified continuously, and social vulnerability (SV) shifted toward moderate dominance as regional integration policies balanced regional development, while comprehensive vulnerability (CV) underwent polarization-concentration-repolarization dynamics under dual natural-social influences. UEPs exhibited significant positive FV correlations, strongest for EE (R = 0.536, p < 0.01) due to flood exposure and facility deficiencies, and weakest for LE (R = 0.387, P < 0.01) with natural drainage advantages. SV correlations remained minimal as social drivers of urban expansion both increased and decreased vulnerability impacts, while NV correlations matched or exceeded CV links. Small expansion patches showed higher vulnerability links than large developments, necessitating prioritized construction of natural flood control infrastructure in small patches. It is necessary to implement drainage retrofits in EE, nature-based water retention in LE, confining IE to flood-protected urban cores, and phasing regional upgrades according to city development stages under integration frameworks, providing transferable solutions for flood-adaptive planning. Future research should refine FV assessment indicators and investigate the lagged effects between UEPs and FV.