Disproportionate increase of flood-exposed population in Chinese cities under urban expansion and climate variation

• A method quantifies future flood-exposed population under climate change and urban expansion. • The compound impacts increase population exposure to flooding in China’s coastal cities. • Controlling urban expansion will reduce future population exposure in eastern China. Coastal cities in China are confronting increasingly severe flood risks, which lead to significant losses of life and property. Here, this study estimate the population exposure to flooding under compounding impacts of climate variation and urban expansion over 1985–2014 and 2021–2100. It finds that the population exposure to flooding is expected to increase by approximately 1.2–4.7 times under such compound impacts. Under the most severe greenhouse gas emission scenario in the future, our projections show that most of China’s coastal provinces, except Shandong Province, will have the largest flood-exposed population. The future flood-exposed population is projected to increase by 2.0 times in Guangdong Province, and by 1.3 times in Liaoning Province compared to the historical period. Additionally, controlling urban expansion will reduce the future flood-exposed population, with the most significant reductions observed in eastern China like Zhejiang and Jiangsu provinces (by 36.2–86.5 %), followed by southern areas like Fujian and Hainan provinces (by 9.8–17.8 %). In contrast, intensified compound extreme heat and precipitation events increase the average flood-exposed population by 21–27 % in Guangdong, Liaoning, and Shandong provinces. Our findings could provide valuable insights to help develop sustainable flood mitigation measures for coastal cities confronting flood risks.