Abstract
In the last decade it has become clear that the timing of many phenological processes, like the start of flowering and leaf unfolding in spring, have changed. The increase in temperature is believed to be the main cause. The earlier start of flowering will have consequences for the start of the pollen season, and thus for the start of the hay fever season. Millions of people worldβwide will therefore experience the impact of climate change in their daily lives during spring and summer. In this paper we analyse the relation between climate parameters, especially temperature, and the start of the pollen season in the western part of the Netherlands based on daily pollen counts of the Leiden University Medical Centre and temperature measurements from 1969 till 2000 by the Royal Netherlands Meteorological Institute in De Bilt. The results indicate that there is a strong correlation between temperature and start of the pollen season. An advance of the start of the pollen season of 3 to 22 days has been observed. The potential future changes in the start of the pollen season under climate change scenarios are also discussed. Copyright Β© 2002 Royal Meteorological Society.