On the origin of summer precipitation variability in the UK

• Main Author: Leeuw, Johannes de
• Published: University of Reading 2014
• Subjects: 551.57
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.646018

Summer precipitation variability is investigated over the England and Wales region. The England and Wales Precipitation dataset (EWP) is an area average estimate derived from rain gauges, taking into account temporal stability and representativeness of the gang<' stations used. The observed daily precipitation distribution is well represented by a Weibull fit. Regional daily precipitation accumulations show large variability over the region, hilt no robust trends are found in mean or extremes over the last 80 years. Comparing the observations with the ERA-Interim short term forecast shows that the ECMWF reanalysis system represents the variability in EWP observations (correlation of 0.91). The shape parameter of the Weibull fit to ERA-Interim precipitation is indistiuguishable from the EWP estimate, but the ERA-Interim estimates are scaled down by 22%. Light precipitation events are overestimated by the ERA-Interim reanalysis. A novel Lagrangian approach is used to investigate monthly precipitation variability during summer for England and Wales. The ROTRAJ trajectory model calculates back trajectories to link precipitation to the origins of water and identifies the evolution of th(' moistun' content of trajectories along their path towards England and 'Vales. Precipitation estimates in the ROTRAJ trajectory model are calculated using specific humidity changes along trajectories in the last 6 hours prior to arrival. The ROTRA'} estimate has similar skill to the ECWMF short term forecast for moderate and extn'llle events (4mm/day), but tends to overestimate the observed light precipitation events (4mm/day) more strongly than the ECI\IWF forecast when compared to EWP.