Meteorological drivers of Japanese cedar pollen deposition across Japan

Pollen allergies pose a growing public health concern, with their severity and distribution influenced by complex seasonal and climatic factors. More than 30% of Japanese adults are allergic to the pollen released by Japanese cedar trees during spring. Although higher summer temperatures have been found to increase pollen dispersal the following spring, the broader influence of year-round meteorological conditions, including temperature, rainfall, and sunshine duration, on pollen dispersal remains poorly understood. This study investigated the impact of temperature, rainfall, and sunshine duration on pollen deposition from Japanese cedar trees at 109 monitoring stations across Japan between 1986 and 2023. We conducted regression analyses using monthly deviations of meteorological parameters with annual total pollen count and the first pollen deposition date as outcome variables. Our results indicate that higher summer temperatures are associated with increased pollen counts in the following year, whereas higher autumn temperatures are associated with reduced pollen counts. Specifically, a 1 °C increase in mean summer (July to September) temperature was associated with a 39.2% (95% CI: 21.9%, 59.0%) increase in annual pollen count, whereas a 1 °C increase in autumn (October to December) temperature was associated with a 12.8% (95% CI: − 22.5%, − 1.9%) decrease. In addition, higher winter rainfall was correlated with reduced pollen counts, and a longer sunshine duration during summer was associated with both an earlier onset and a larger amount of pollen deposition. These findings underscore the importance of considering how meteorological conditions across years influence pollen deposition in various regions when evaluating the potential effects of climate change on human health through pollen exposure.