Heavy rainfall on the increase

Scientists at the University of East Anglia (UEA) have found that winter precipitation – such as rain and snow - became more intense in the UK during the last 100 years.

Similar increases in heavy rainfall have now also become evident in spring and, to a lesser extent, autumn.

A previously reported reduction in heavy summer rainfall appears to have ended during the 1990s, with observations for the last decade indicating a return to more typical amounts of intense rainfall in summer.

The results will inform other work currently being carried out on flood risk and the impact of extreme weather events. As surface run-off depends on rainfall intensity and frequency, changes in intense rainfall events will impact strongly on floods.

The UEA study was funded by the Natural Environment Research Council (NERC) as part of the Flood Risk from Extreme Events (FREE) programme, which aims to improve predictions of floods minutes-to-weeks and seasons-to-decades ahead, by using environmental science to investigate the physical processes involved in generating extreme flooding events.

Using data from more than 600 rain gauges around the UK, from as far back as 1900 to as recently as 2006, Douglas Maraun, Tim Osborn and Nathan Gillett, of the university’s Climatic Research Unit, classified every day’s measured precipitation into one of 10 categories of rainfall intensity, from drizzle to a downpour. They then analysed how the amount of precipitation in each category has changed over time. In winter, for example, the amount of precipitation falling in the heaviest category has increased over the last 40 years in all regions of the UK.