Wet-hot days increased faster than dry-hot days during the warm season in Chinese cities over the past four decades

Abstract

As global urbanization accelerates, its potential impact on compound temperature-humidity extremes has become a critical concern for sustainable urban development. Here we examine spatiotemporal trends and urbanization effects on dry-hot and wet-hot extremes during the warm season (May-September) across 136 Chinese cities from 1981 to 2022. Results show a significant increase in both compound extremes, with wet-hot days rising faster (1.5 days per decade) than dry-hot days (0.3 days per decade). Amplification indices reveal that wet-hot coupling dominates, accounting for 36% of all hot days, while dry-hot coupling is relatively rare (4%). However, the mounting dry-hot amplification index indicates that extreme heat is increasingly coupled with drought. Urbanization, driven by impervious surface expansion and vegetation loss, intensifies both extremes, especially during rapid urbanization phases. These findings underscore the urgent need for adaptive urban strategies to mitigate the growing risk of compound temperature-humidity extremes under ongoing urbanization and climate change. Compound temperature-humidity extremes represent a growing risk across 136 cities in China, with wet-hot days accounting for 36 percent of all hot days, while dry-hot days are rare, according to an analysis that combined urban, climate, and land use data.

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