There is a widely-held view that future climate change will increase flood risk in the UK. Extensive modelling studies have been undertaken at CEH to test this hypothesis. The development of continuous river flow simulation techniques for flood frequency estimation now provides a new methodology to predict climate change impacts on flood flows. This technique has been applied to a range of British catchments (work funded by the UK Department for the Environment, Food and Rural Affairs) to assess potential changes in flood risk and directly inform policy development for flood defence scheme appraisal. Using observed climate variables and river flows, the catchment models have been calibrated and validated for the present day. A wide range of climate change scenarios have then been applied to the driving climate data and river flow time series simulated indicative of future time horizons. The flood characteristics of the future have been compared with those of the current. There are many uncertainties associated with this type of climate change impact analysis, including the choice of which Global Climate Model (GCM) to use to derive scenarios of change and precisely how coarse-resolution climate changes (from GCMs) are downscaled to the catchment level, as well as hydrological modelling uncertainty. These uncertainties have been assessed, and their effects on the results are discussed. Despite the belief that flood flows will increase in the future, there is no clear message about the size, or even the direction of change in flood flow magnitudes in the UK. Changes in flood flows are catchment-specific, being driven by hydrological variability, such as geology, and the seasonal distribution of rainfall.
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