The FORGEX method of rainfall growth estimation - III: Examples and confidence intervals

This paper illustrates the performance of the FORGEX method of rainfall growth estimation. Results are presented for three regions of the United Kingdom: the East Midlands, north-west England and south-west England. Focused rainfall growth curves are compared between regions and between different sites within each region. Typical growth curve shapes are discussed with reference to the climate of each region. Daily growth curves are derived from a large number of records of annual maximum rainfalls. A smaller number of hourly annual maximum series is available for estimating sub-daily rainfall growth curves. Rainfall growth rates are compared with the results of a widely used method. The present method allows more local and regional variation in growth rates. The new growth rates are higher for durations of 1 and 2 days in parts of south-west England, but lower for moderate return periods at some focal points in the north-west. In the East Midlands, the new 1-hour growth rates are considerably higher for long return periods. Confidence limits for growth rates are derived by bootstrapping. This is accomplished by fitting a large number of growth curves to resampled sets of rainfall data.