Fine-Scale Assessment of Inequalities in Emergency Shelter Accessibility Using the 3SFCA Method: A Focus on Distributional Balance and Lower-Tail Welfare

With climate change and urbanization accelerating, cities face increasing disaster risks. As critical facilities for safeguarding residents’ safety, emergency shelters have attracted growing attention due to spatial supply–demand mismatches. From the perspective of the 15-min community life circle, this study aims to develop a fine-scale analytical framework for assessing emergency shelter accessibility and inequality, using Pidu District, Chengdu, China, as a case study. The three-step floating catchment area (3SFCA) method is applied to assess emergency shelter accessibility, while the Gini coefficient and Kolm–Pollak equally distributed equivalent (EDE) are introduced to evaluate accessibility inequality across subdistricts and communities. The results show that: (1) compared with the traditional Gaussian two-step floating catchment area (G2SFCA) method, 3SFCA captures clearer accessibility differentiation and stronger local sensitivity; (2) emergency shelter accessibility shows marked spatial differentiation, with pronounced local clustering in the walking mode and a polycentric pattern in the cycling mode; (3) the Gini coefficient reveals distributional imbalance in emergency shelter accessibility, showing a clear “center–periphery” pattern in which urban areas generally exhibit lower inequality than suburban and rural areas; and (4) the Kolm–Pollak EDE emphasizes lower-tail welfare and helps distinguish “low but even” areas from “high but polarized” areas. These findings support equity-oriented strategies for emergency shelter planning and resource allocation. The study provides methodological and practical implications for fine-scale emergency shelter planning and resilient urban governance, contributing to more equitable, inclusive, resilient, and sustainable urban environments.