Changes in drought frequency, severity and duration for the British Isles projected by the PRUDENCE regional climate models

SummaryUsing multiple climate models for impact assessment allows the examination of uncertainty in projections of change, thus providing improved tools for the adaptation and mitigation of the impacts of future change. Here, the performance of integrations from six regional climate models (RCMs) driven by four different general circulation models (GCMs) have been assessed for British Isles mean precipitation and drought statistics for the 1961–1990 period, using two drought severity indices based on monthly precipitation anomalies. Spatially averaged statistics are examined in addition to spatial variations in model performance over water resource regions and compared with observations. Estimates of the range and sources of uncertainty in future changes are examined for the SRES A2 2071–2100 emissions scenario.Results indicate that the RCMs are able to reproduce the spatially averaged annual precipitation cycle over the British Isles but the spatial anomalies suggest that they may have difficulty in capturing important physical processes responsible for precipitation. The RCMs are unable to simulate the observed frequency of drought events in their control climate, particularly for severe events, possibly due to a failure to simulate persistent low precipitation. Future projections suggest an increase in mean precipitation in winter and decrease in summer months. Short-term summer drought is projected to increase in most water resource regions except Scotland and Northern Ireland, although the uncertainty associated with such changes is large. Projected changes in longer droughts are influenced by the driving GCM and are highly uncertain, particularly for the south of England, although the longest droughts are projected to become shorter and less severe by most models. This suggests that many water supply companies may need to plan for more intense short-term droughts but may experience fewer longer duration events under future climate change.