Urban cloud coverage anomaly indicates increasing impacts mainly in developing economies

Quantifying changes in cloudiness is crucial for understanding future atmospheric dynamics. Human activities may drive such changes, yet their role remains poorly characterized within a global framework. Using worldwide satellite observations, here we assessed cloud coverage trends at both regional (IPCC-defined regions) and local scales, focusing on 226 megacities ( > 1M inhabitants) and 146 midsize cities (0.1-1M). Our findings reveal that: 1) Irrespective of the sign of significant regional trends, the local scale analysis exhibits mainly significant increasing trends of cloud coverage anomaly. 2) Developing economies exhibit the strongest signals: 55-62% of megacities and 42-44% of midsize cities with demographic growth show significant upward trends, particularly coastal cities in tropical climates, underscoring the interaction between urbanization and background climate. 3) Seasonal analyses highlight a stratification of trends by climatological zone, with 64% of megacities exhibiting at least one significant seasonal trend compared to 47% for annual trends. Cloud coverage over cities is increasing, especially those in developing countries, with coastal cities in tropical climates exhibiting the most significant increases, according to analyses of global-scale satellite cloud coverage data.