Climate Change Impacts on Irish River Flows: High Resolution Scenarios and Comparison with CORDEX and CMIP6 Ensembles

Climate change is likely to impact water quality, resource availability and riverine ecosystems. While large ensembles are available to assess future impacts (e.g., the Coupled Model Intercomparison Projects (CMIP) and/or CORDEX) many countries have developed their own high-resolution ensembles. This poses a selection problem with robust adaptation dependent on plausible ranges of change being adequately quantified. Therefore, it is important to compare projected changes from available ensembles. Here we assess future climate change impacts for 26 Irish catchments. Using a high-resolution national ensemble of climate models projected impacts in mean, low and high flows are assessed and uncertainties in future projections related to catchment size. We then compare future impacts from CORDEX and CMIP6 ensembles for a subset of catchments. Results suggest increases in winter flows (-3.29 to 59.63%), with wide ranges of change simulated for summer (-59.18 to 31.23%), low (-49.30 to 22.37%) and flood (-19.31 to 116.34%) flows across catchments under RCP8.5 by the 2080s. These changes would challenge water management without adaptation. Smaller catchments tend to show the most extreme impacts and widest ranges of change in summer, low and flood flow changes. Both the ensemble mean and range of changes from the national ensemble were more modest and narrower than the CMIP6 and CORDEX ensembles, especially for summer mean and low flows, highlighting the importance of evaluating impacts across ensembles to ensure adaptation decisions are informed by plausible ranges of change.

Automated summary

Climate change could impact water quality, resource availability, and riverine ecosystems. Comparing projected changes from different ensembles is important for robust adaptation, as different ensembles could yield wide ranges of change. This study evaluates future climate change impacts on 26 Irish catchments, comparing impacts from a national ensemble, CORDEX, and CMIP6 ensembles. Results indicate increasing winter flows and wide ranges of change in summer, low, and flood flows across catchments under RCP8.5 by the 2080s. Smaller catchments show more extreme impacts and wider ranges of change. The national ensemble shows more modest and narrower changes compared to CMIP6 and CORDEX ensembles, emphasizing the importance of evaluating impacts across ensembles for informed adaptation decisions.