Cumulative temperatures for prediction of the beginning of ash (Fraxinus excelsior L.) pollen season

The aim of this study is the analysis of the meteorological conditions leading to the release of ash pollen in order to predict the beginning of the pollen season in Zurich, Switzerland. For 12 years over a period of 14 consecutive years, it appears that ash pollen release begins when the cumulated mean daily temperatures starting on January 1 reach 220.7°C, admitting a variation of ±30°C that more or less corresponds to 3 consecutive days at 10°C.