Long-term changes in the timing and intensity of the pollen season in Slovenia (2002 – 2024)

Climate change is reshaping pollen season dynamics across Europe, with significant implications for allergic populations. This study presents the first comprehensive long-term analysis of pollen season trends in Slovenia, a region characterized by high phytogeographic diversity at the intersection of Mediterranean, Alpine, Dinaric, and Pannonian climatic influences. Daily airborne pollen concentration data from three monitoring stations were analyzed for 18 allergenic taxa over 23 years (2002-2024). Pollen season timing was determined using a normalized cumulative-sum approach, and linear regression quantified temporal trends in season onset, termination, duration, and total annual pollen load. Results reveal general advancement in season onset across most taxa, particularly pronounced for early-blooming arboreal species in the Mediterranean region. Season termination exhibited asymmetric patterns: earlier endings for spring-flowering trees and delayed termination for herbaceous taxa, especially Poaceae. Notably, early blooming trees showed compressed seasons due to faster advancement of season end relative to onset, potentially leading to more intense allergen exposure despite shorter duration. Significant increases in annual pollen load were detected for Poaceae, Urticaceae, and Plantago , while Artemisia showed widespread decline. The coastal Mediterranean site exhibited significantly earlier onset, later termination, and longer seasons compared to continental stations, which showed strong inter-site synchrony. These findings demonstrate asymmetric phenological responses to climate forcing across small spatial scales, with important implications for region-specific public health strategies.