Climate-change impacts on river flows in Britain: The UKCIP02 scenarios

This paper describes the implications of the UKCIPO2 climate-change scenarios for river flows in Britain, focusing on mean monthly runoff and Q95 (i.e. the flow which is exceeded for 95% of the time). By the 2020s, mean summer flows will be about 30% lower than the 1961-1990 mean, and 095 will be reduced by approximately 25%. Percentage reductions are particularly large in southern and eastern England. Mean winter flows are modestly increased, with the greatest increases in the north and west. Reductions in the recharge season result in lower flows in groundwater-dominated catchments throughout the year. The climate-change signal is larger than natural multi-decadal variability-even by the 2020s. This natural variability can add +/- 5% to the changes in Q95 due to climate change. Changes resulting from the UKCIPO2 scenarios are (a) more extreme during summer than those resulting from earlier climate-change scenarios, showing considerably greater flow reductions, and (b) at the drier end of the range in changes arising from the application of scenarios based on other coarser-resolution climate models.