The FEH13 rainfall DDF model was based on an analysis of over 170,000 station-years of data from daily rain gauges throughout the UK, together with about 17,000 station-years of hourly data. It was developed to allow the estimation of rainfall depths falling over durations from 1 hour to 192 hours (8 days) for return periods ranging from 2 years to over 10,000 years. The FEH13 model has been extrapolated to provide depth estimates for durations as short as 5 minutes and return periods as frequent as 12 months (estimated on the peak-over-threshold (POT) scale).

The FEH13 model was released via the FEH Web Service in 2015 and is based on rain gauge records up to about 2005. The original research was funded by Defra (FD2613) and aimed to develop revised rainfall frequency estimates for the longest return periods of relevance to reservoir spillway safety assessment (Stewart et al., 2013). UKCEH funded the further development and generalisation of FEH13 for the full range of durations (from less than 1 hour to 8 days) and return periods (from 12 months to over 10,000 years). Recent research funded by the Environment Agency and UKCEH has investigated the impact of including more recent extreme rainfall events in the model calibration in a case study of Cumbria (Vesuviano et al., 2021). Record-breaking rainfall events were experienced in the region in November 2009 and December 2015, and these together with other events that led to severe flooding were included in the recalibration of FEH13. The results suggest that extreme events of durations between 2 and 4 days are estimated to have shorter return periods (i.e. to be relatively more frequent) in the recalibrated model than estimated by the original FEH13 model (Vesuviano et al., 2021). However, it is important to recognise that a high level of uncertainty still remains in defining return periods in the hundreds or thousands of years using relatively short observational records.

As part of the FEH Research Programme, UKCEH has recalibrated the FEH13 model across the UK using more recent rain gauge records for a range of durations; FEH22.