Is the changing precipitation regime of Manchester, United Kingdom, driven by the development of urban areas?



Precipitation measurements made at three weather stations and one composite record from the Manchester region and the Isle of Man have been analysed over the period 1899–2008. Large positive trends over the last 40 years were identified for the three records within 50 km of Manchester whilst the Isle of Man measurements revealed no such trend. The recent increase in rainfall at the urban or urban-influenced sites was significantly and negatively correlated with NOx emissions recorded in Manchester whilst local temperature and atmospheric circulation indices appeared to be largely unrelated. Sea surface temperature in the precipitation source region was also significantly related to annual precipitation levels. Further evidence for an urban influence was investigated but an analysis of back trajectories (BTs) showed only a slight increase in rainfall on the days where the trajectories tracked back past an urban centre. However, the discovery of a weekly cycle in the precipitation increase suggests that an urban influence should not be ruled out. The complicated factors driving this distinctive rainfall trend require further investigation so that water resources and flood impacts can be managed more effectively in the future. Copyright © 2011 Royal Meteorological Society