The start of the grass pollen season is compared over a network of standard sites for the six year period, 1987#x2013;1992. Five sites have records for the whole of this period, and a further four joined the network at different times since 1987. Two definitions of the start of the season were compared; those defined by the sum75 method tend to be later than those defined by the 98 method. Differences in the start dates were analysed in relation to cumulative temperatures above 5.5#xB0;C and monthly total rainfall from February to the end of June. Where comparisons can be made, seasons often start simultaneously in the south and the west. The variation in start dates shows a close relationship to cumulative temperatures and to rainfall in May and June but the patterns are complicated. Future work will analyse the data from the full geographical range of the network now that more sites are operating.
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