Heatwaves in Hong Kong and their influence on pollution and extreme precipitation

Recently, the frequency of heatwaves has increased worldwide, with significant implications for public health, the environment, and socio-economic stability. In densely populated urban areas such as Hong Kong, heatwave events are of particular concern owing to their potential to exacerbate air pollution and modulate weather patterns, including extreme precipitation events. Despite extensive research on these phenomena, there exists a gap in understanding the interconnections of heatwaves, pollution, and extreme precipitation in subtropical urban climates. Utilising in-situ meteorological data from the Hong Kong Observatory (HKO), we investigated the characteristics of heatwaves and explored their impact on pollution and local rainfall. We observed a significant increase in the frequency, intensity, and duration of heatwaves in Hong Kong, particularly after 2010. Synoptic analysis indicates that these heatwaves are often associated with persistent high-pressure systems or tropical cyclones periphery downdrafts, as these patterns could induce subsidence and reduce cloud cover, which contributes to temperature increase. Additionally, heatwaves significantly elevated concentrations of ground-level ozone and particulate matter owing to increased photochemical reactions and stagnant air conditions. These pollution spikes coincide with heatwaves, aggravating public health risks. Furthermore, the increased frequency of heatwaves has altered the composition of local precipitation, with heatwave-following extreme precipitation events occurring more frequently, suggesting a thermal-driven amplification of the hydrological cycle. Our results highlight the urgent need for integrated urban planning and health policies that address the compounding effects of heatwaves, pollution, and subsequent extreme precipitation, underscoring the importance of adapting to and mitigating these linked phenomena amid a changing climate.