Use of very high resolution climate model data for hydrological modelling: baseline performance and future flood changes

Increasingly, data from Regional Climate Models (RCMs) are used to drive hydrological models, to investigate the potential water-related impacts of climate change, particularly for flood and droughts. Generally, some form of further downscaling of RCM data has been required, but recently the first decadal-length runs of very high resolution RCMs (with convection-permitting scales) have been performed. Here, a set of such runs for southern Britain has been used to drive a gridded hydrological model. Results using a 1.5km RCM nested in a 12km RCM driven by European-reanalysis boundary conditions show that the 1.5km RCM generally performs worse than the 12km RCM for simulating river flows in 32 example catchments. The clear spatial patterns of bias are consistent with bias patterns shown in the RCM precipitation data. Results using 1.5km and 12km RCM runs for the current climate and a potential future climate (driven by GCM boundary conditions) show clear differences in projected changes in flood peaks. The 1.5km RCM tends towards larger increases than the 12km RCM, particularly in spring and winter. If robust, this could have important consequences for adaptation planning under climate change, but further research is required, particularly given the greater biases in the baseline flow simulations driven by 1.5km RCM data, and the use of only a single short future climate projection.