Using regional climate model data to simulate historical and future river flows in northwest England

Daily rainfall and temperature data were extracted from the multi-ensemble HadRM3H regional climate model (RCM) integrations for control (1960-1990) and future (2070-2100) time-slices. This dynamically downscaled output was bias-corrected on observed mean statistics and used as input to hydrological models calibrated for eight catchments which are critical water resources in northwest England. Simulated daily flow distributions matched observed from Q(95) to Q(5), suggesting that RCM data can be used with some confidence to examine future changes in flow regime. Under the SRES A2 (UKCIP02 Medium-High) scenario, annual runoff is projected to increase slightly at high elevation catchments, but reduce by similar to 16% at lower elevations. Impacts on monthly flow distribution are significant, with summer reductions of 40-80% of 1961-90 mean flow, and winter increases of up to 20%. This changing seasonality has a large impact on low flows, with Q(95) projected to decrease in magnitude by 40-80% in summer months, with serious consequences for water abstractions and river ecology. In contrast, high flows (> Q(5)) are projected to increase in magnitude by up to 25%, particularly at high elevation catchments, providing an increased risk of flooding during winter months. These changes will have implications for management of water resources and ecologically important areas under the EU Water Framework Directive.