A comparison of hydrological impacts from two ensembles of regional climate projections with a range of climate sensitivities

Understanding the range of potential impacts of climate change is crucial for appropriate adaptation planning, especially for floods and water resources. Driving hydrological models with data from climate models provides important information, but can be limited by availability and useability of appropriate climate ensembles for the region of interest. Here, a recently re-processed multi-model ensemble of regional climate projections, derived from Euro-CORDEX, has been used alongside a regional perturbed parameter ensemble, from UK Climate Projections 2018, to drive a national-scale grid-based hydrological model, to assess future impacts on river flows across Great Britain. The results show relatively consistent increases in GB-median winter flows and 5-year return period high flows, but the magnitude of GB-median decreases in summer flows is more different between the two ensembles, as are reductions in 5-year return period low flows. The signs of GB-median changes in spring and autumn flows are inconsistent. Spatial patterns of change also show significant differences between ensemble members. Assuming the climate model results are all plausible, adaptation planning for Britain should take account of impacts from a range of climate models to enable more robust long-term decision-making for water management. Flow changes assessed using fixed baseline and future time-slices differ from those using time-slices derived by model-based global temperature change from the pre-industrial period; the latter removes some uncertainty related to choice of emissions scenario and improves comparability between different climate models, but the preferred approach may depend on the application.