Comparison of two hourly to 5-min rainfall disaggregators

A disaggregation method used by the UK water industry to disaggregate simulated hourly data to the 5-min time-scale is examined using data from Heathrow (London). This analysis shows the shortcomings of this algorithm, both in reproducing the temporal structure of rainfall depths and generating extreme events. An alternative method is proposed, based upon a random cascade with a log-Poisson generator. This is a parsimonious model requiring only two parameters per season. It is shown to provide a clear improvement upon the existing disaggregator, both in terms of temporal structure and extreme behaviour. It could thus be a powerful tool for urban hydrology which requires data at fine time-scale for design purposes and simulation studies. The utility of such a tool depends upon its potential for operational use, i.e., for implementation without any fine-scale data. The model's performance is found to be maintained when hourly rainfall time series are the only available data.