Effects of climate change on pollen season features of herbaceous species in the Milan area, Northern Italy

Different herbaceous plant species release allergenic pollen that can have adverse effects on human health. Climate change, which alters plant physiology and phenology, can affect airborne pollen levels, increasing the risk for allergy sufferers. This study examines trends in airborne pollen concentrations and seasonal characteristics, aiming to identify potential shifts in the onset, end, and duration of the main pollen seasons of herbaceous plant species over the last few decades, with particular attention to exploring the association between phenological changes and climate parameters. Moreover, forecasting scenarios of pollen season features trends concerning the meteorological variables we presented. To this purpose, data from the aerobiological station of the Milan area (Legnano, Lombardy, Italy), located in one of the most invaded parts by Ambrosia artemisiifolia in Italy and Europe, and characterized by a time series of nearly 30 years, from 1995 to 2022, were analysed. The results showed a clear correlation between main pollen season features and meteorological variables for Poaceae, Urticaceae, Artemisia and Ambrosia. Generally, increasing temperature and solar radiation were linked to an anticipated onset of the pollen season, while precipitation and relative humidity to an earlier end date. Moreover, in the study areas, a strong increase in annual average temperature has been observed since 1975, projected to continue over the next 60 years. This increase was predicted to lead to an earlier start and longer duration of the pollen season for weed species, potentially advancing by up to 2 weeks over 60 years. These findings indicate an elevated risk of exposure for individuals with allergies in the short term and underscore the urgent need to implement long-term monitoring frameworks for both ecological and public health purposes.