Estimating probable maximum precipitation using a storm model approach

An approach to estimating probable maximum precipitation (PMP) using a simple, totally objective, storm model of convective systems is outlined. PMP hyetographs are compared with observations for severe events, and the variation of storm model PMP with storm duration is compared with PMP values derived using the UK Flood Studies Report (FSR) (NERC, 1975, Department of the Environment, London) approach. The storm model generates PMP values very similar to the FSR for storm durations less than 11 h, but for durations between 11 and probably 24 h the FSR PMP values are exceeded. It is suggested that longer duration events may be associated with mesoscale convective systems (MCSs), which have only been recognised in the UK since the FSR was published.