Catchment characteristics for index flood regionalisation

Flood frequency regionalisation for ungauged catchments depends on relevant catchment characteristics. In this study, alternative catchment characteristics for south-west England were derived using the data freely downloadable from the internet. It was found that the alternative catchment characteristics were more heterogeneous than the Flood Estimation Handbook (FEH) catchment descriptors. Therefore, they suffered less in information redundancy and had a potential to produce more reliable regression models. The results have demonstrated that the model from the alternative catchment characteristics had a better performance than the FEH model and FEH local model. It is also useful to note that a recalibrated FEH local model had a poorer performance than the original FEH model. This indicates that a national model should not simply be recalibrated using a regional data set. The methodology and catchment characteristics used in the present study are more applicable to other parts of the world than the catchment descriptors in the FEH due to the easier data access used in the present study.