Design flood flows with climate change: method and limitations

Abstract

An extended method is presented for ‘perturbing' design flood flows to account for climate change. Specifically, the method uses climate model output to directly alter parameters in the UK Flood Estimation Handbook rainfall–runoff model. The method is explored using a model of the River Eden catchment in northwest England, which comprises 26 sub-catchment hydrological models, with outflows routed using a hydraulic model. The results show a significant increase in flood flows and water levels by the 2080s, although uncertainties are large. The size of the increases varies depending on the climate change scenario and timing of the event, with the monthly precipitation change factor the single largest determinant of the change in peak flow. The method is reasonably simple to apply and there are benefits of using climate model information, rather than a sensitivity allowance, in terms of geographical interpretation of changes in precipitation and explicit representation of some of the uncertainty related to climate change. However, there are significant limitations to the methodology, in particular the minimal representation of antecedent conditions and more generally due to the ability of climate models to accurately reproduce and simulate extreme precipitation.