Assessment of the return period of near-PMP point and catchment rainfall for England and Wales

The return periods of sub-daily rainfall events approaching Probable Maximum Precipitation (PMP) have been estimated for point locations and catchment areas using the assumptions made in a previously published storm model. It has been assumed that PMP of around 12 h duration is the result of severe thunderstorms for catchments up to about 200 km2 and of mesoscale convective systems (MCSs) for larger catchments. The analysis suggests return periods ranging from around 1 in 10 000 years for point locations to 1 in 500 000 years for large catchments, though these are very dependent on the assumptions. The results are compared with estimates from a number of other sources. Copyright © 2010 Royal Meteorological Society