Variability and trends in England and Wales Precipitation

6 The England and Wales Precipitation (EWP) dataset is a homogeneous time series of 7 daily accumulations from 1931 to 2014, composed from rain gauge observations spanning 8 the region. The daily precipitation statistics are shown to be well described by a Weibull 9 distribution, which is used to define extremes in terms of percentiles. Computed trends in 10 annual and seasonal precipitation are sensitive to the period chosen, due to large variability on 11 interannual and decadal timescales. Atmospheric circulation patterns associated with seasonal 12 precipitation variability are identified. These patterns project onto known leading modes of 13 variability, all of which involve displacements of the jet stream and storm-track over the eastern 14 Atlantic. 15 The intensity of daily precipitation for each calendar season is investigated by partitioning 16 all observations into 8 intensity categories contributing equally to the total precipitation in 17 the dataset. Contrary to previous results based on shorter periods, no significant trends of 18 the most intense categories are found between 1961-2014, except for a small negative trend in 19 the most extreme category of summer precipitation. The area-average precipitation is found 20 to share statistical properties common to the majority of individual stations across England 21 and Wales used in previous studies. 22 Statistics of the EWP data are examined for multi-day accumulations up to 10 days, which 23 are more relevant for river flooding. Four recent years (2000, 2007, 2008 and 2012) have a 24 greater number of extreme events than any previous year in the record. It is the duration of 25 ∗Correspondence to: J. de Leeuw, Department of Meteorology, University of Reading, Earley Gate, PO Box 243, UK. Email: [email protected] †[email protected] ‡[email protected] 1 precipitation events in these years that is remarkable, rather than the magnitude of the daily 26 accumulations. 27