How might climate change affect river flows across the Thames Basin? An area-wide analysis using the UKCP09 Regional Climate Model ensemble

The Thames Basin drains an area of over 10,000 km2 through London to the North Sea. It encompasses both rural and heavily urbanised areas overlying a spatially-varied and complex geology. Historically, the lower Thames has proved resilient to climate variability, and careful river management in recent years has helped protect the region from flooding. However, recent climate projections for the region indicate that over the next century winter rainfall might increase by 10–15%, potentially leading to higher flows than the Thames can accommodate. This study uses a distributed hydrological model, the Grid-to-Grid (G2G), to assess future changes in peak river flows for a range of catchments across the Thames Basin. The G2G model has used as input an ensemble from the UK Climate Projections (UKCP09) Regional Climate Model (RCM), under the A1B emissions scenario, to analyse changes in flood frequency between two 30-year time-slices (October 1960–September 1990 and October 2069–September 2099). The RCM ensemble uses a perturbed-parameter approach to address uncertainty in climate projections.