Types of pollen season depending on the weather conditions in Wrocław (Poland), 2002-2011.

The aim of the study was to characterise pollen season types according to weather conditions in Wrocław (south-western Poland) in the years 2002-2011. Over the period analysed, the start date of the pollen season (determined by the 95 % method) ranged from 10 July 2002 to 28 July 2010. The start date of the pollen season can be determined by using Crop Heat Units (CHUs). During the period 2002-2011, the pollen season started after the cumulative value of CHUs had reached 2,000-2,100 °C. The three distinguished types of pollen season are best described by the frequency of weather types defined by the type of circulation, mean daily air temperature, and the occurrence of rain. The variation in these factors affected the dynamics of the pollen season. The noteworthy frequency of days with rain and high seasonal sum of precipitation totals as well as the dominance of cyclonic weather from the westerly direction had an impact on the extension of the pollen season. The meteorological factors that directly affect pollen release and transport primarily include air humidity, expressed as vapour pressure ( > 0.3,  < 0.01), temperature( from 0.2 to 0.4,  < 0.01). The relationships between averaged meteorological data and daily pollen concentration were stronger ( > 0.5,  < 0.01). Based on the correlation analysis, the meteorological variables were selected and regression equations were established using stepwise backward regression analysis.