Global escalation of humid heat extremes: a hot topic in climate change research

The occurrence of extreme heat episodes has indicated a major shift in recent times, often characterized by high temperatures coupled with abnormally elevated levels of humidity. These high wet-bulb temperatures have tested the human survival thresholds. Consequently, climate scientists and researchers have investigated various complex interplays of humid heat extremes (HHEs) in urban environments. This study employs bibliometric analysis to explore myriad dimensions of HHEs through a systematic literature review of 823 articles published till December 2024. The analysis reveals research trends while identifying hotspots and synthesizing key themes in the steadily growing scientific literature on HHEs. A refined search query retrieved relevant articles (n=87) across multiple domains, covering facets of physical mechanisms, synoptic patterns, geographic distribution, and human health impacts. The findings highlight the rapid emergence of HHEs as a dynamic and complex meteorological phenomenon, with a notable surge in research since 2018. China leads in publication output (77.02%), followed by the United States and Europe. The review attributes the rise in HHEs to climate change, increased anthropogenic activities, declining vegetation cover, and unprecedented shifts in urban energy balance. It further advocates the necessity of humidity-sensitive urban planning, enhancement of urban resilience strategies, and urges for more biometeorological investigations to better understand health impacts and mitigate the challenges of moist heat stress. By integrating humidity into public health policies, epidemiological research, and urban planning, this study provides a comprehensive understanding of HHEs while outlining future research prospects. This study serves as a valuable resource for researchers seeking insights into the evolving landscape of humid heat studies and their broader implications.