Weather sets airborne pollen dynamics in motion: a five-year case study from northeastern Croatia

Weather is the main factor influencing pollen dynamics and the onset of the pollinosis season in sensitised populations. To assess these patterns, a five-year study (2019–2023) tracked pollen concentrations in Vinkovci, northeastern Croatia, using the Burkard volumetric trap. Pollen sample preparation followed the British Aerobiology Federation protocols, while meteorological data were obtained from the Croatian Meteorological and Hydrological Service. Spearman's correlation analysis assessed the relationship between weather conditions and pollen concentrations. Additionally, multi-year seasonal pollination patterns were heatmap visualised using the National Allergy Bureau scale. Overall, 61,657 pollen grains/m³ were recorded from 61 taxa. Within this spectrum, weeds made up the largest proportion (58%), followed by trees (36%) and grasses (6%). The highly allergenic species, Ambrosia artemisiifolia, was the most prevalent (27%), narrowly outranking the moderately allergenic genera Urtica (26%) and Betula (11%). Minimal interannual variation was observed for A. artemisiifolia, with concentrations consistently reaching high-to-very-high levels in mid-to-late August. The Betula spp. pollination peaked in late March and early April, ceased by June, while Urtica spp. pollinated from April to September, with an extended summer season. The seasonal pollen distribution (SPD) was strongly affected by weather. Specifically, A. artemisiifolia_SPD correlated positively with temperature (ρ₂₀₁₉ = 0.563, p < 0.001; ρ₂₀₂₂ = 0.423, p < 0.01) but negatively with rainfall (ρ₂₀₂₂ = – 0.420, p < 0.01). Likewise, Urtica_SPD was consistently and positively associated with temperature (ρ_2023-peak = 0.545, p < 0.001), whereas rainfall had a washing-off effect (ρ₂₀₁₉ = – 0.272, p < 0.01; ρ₂₀₂₃ = – 0.214, p < 0.05). Conversely, Betula_SPD showed both negative (ρ₂₀₂₁ = – 0.469, p < 0.001) and positive (ρ₂₀₂₃ = 0.568, p < 0.001) correlations with temperature. These findings provide an important baseline for pollen forecasting amid climate change, as rising temperatures may extend pollination season and increase both allergy risk and associated healthcare costs.