Developing FEH methods - a new model of rainfall frequency

This paper describes recent Joint Environment Agency/Defra-funded research to develop a new model of rainfall depth-duration frequency (DDF) for the UK to replace the current, widely-used Flood Estimation Handbook (FEH) model. The new model is based on the analysis of annual maxima derived from a large number of daily and hourly raingauges throughout the UK, and the results are applicable to rainfall durations from 1 hour to 8 days and for return periods from 2 to over 10,000 years. Differences with the FEH results are generally modest for return periods less than 200 years. However, estimated rainfalls for longer return periods tend to be lower than those derived from the FEH except in Scotland, where estimates for the shortest durations have increased. A follow-on project starting in the near future will incorporate the new DDF model into a revised software utility to replace that currently available on the FEH CD-ROM 3.