Bridging the Cold Divide: Mapping and Mitigating Undercooling Inequities in Southern China’s Rural Homes

The risk of indoor undercooling during winter in rural southern China poses a significant challenge to health and equity, with substantial spatial disparities driven by climatic variation and the absence of heating infrastructure. This study quantifies undercooling risk and spatial inequity across 78 rural regions using Typical Meteorological Year (TMY), simulation-based analyses, with the Indoor Undercooling Hour (IUH), Indoor Undercooling Degree (IUD) and the Gini coefficient as key indicators. Results show that indoor undercooling in self-built rural dwellings is widespread, with the lower and middle reaches of the Yangtze River, the Yangtze River Delta, and high-altitude south-western regions being particularly affected. Marked inequities are observed, reflected by Gini values for IUH and IUD of 0.46 and 0.58, respectively. Pronounced disparities exist across regions in both undercooling risk and socio-economic and demographic conditions, with south-western regions experiencing heavier health inequities due to smaller populations and weaker economies. Passive retrofit strategies can substantially reduce undercooling; however, exclusive reliance on them may exacerbate inequity among regions. Accordingly, active measures, such as centralized heating, are recommended in high-risk areas to promote health and equity.