Flood frequency estimation by continuous simulation under climate change (with uncertainty)

This paper explores the potential for assessing the impacts of climate chan ge upon flood frequency for the gauged, upland Wye catchment at Plynlimon, Wales, UK, while taking account of uncertainty in modelling rainfall-runoff processes under current conditions. A continuous simulation methodology wh ich uses a stochastic rainfall model to drive the rainfall-runoff model TOP MODEL is utilised. Behavioural parameter sets for both the rainfall model a nd TOPRMODEL are identified prior to the climate change runs using the Gene ralised Likelihood Uncertainty Estimation (GLUE) methodology. The "medium-h igh" UKCIP98 climate change scenario, obtained from the HadCM2. GCM simulat ions, is used as a starting point for a variety of different scenarios at t he catchment scale. It is demonstrated that while the scenarios have only a small impact upon the likelihood weighted flood frequency uncertainty boun ds in comparison with the current condition scenario, the risk of a given d ischarge as an element in the distribution of T year floods is changed. Thi s underlines the need to account explicitly for uncertainty within hydrolog ical modelling, especially in estimating the impacts of climate change.