Climate change impact on hydrological droughts: differences between two ensembles of regional climate projections across Great Britain

•Region: This is a national-scale study covering Great Britain.
•Focus: Understanding the impact of climate change on hydrological droughts, and the uncertainty surrounding these projections, is crucial to support water resources management and adaptation planning. Research indicates potentially severe increases in hydrological drought for Great Britain, but most studies are underpinned by a single climate model structure through the widespread use of UKCP18 Regional projections. Here, we compare changes to hydrological droughts modelled using two different ensembles of regional climate projections (the EuroCORDEX-UK multi-model ensemble and the UKCP18 Regional perturbed-parameter ensemble) as input to a national-scale gridded hydrological model.
•New Hydrological Insights: We find considerable differences in drought projections between the two ensembles, with UKCP18 Regional generally indicating more extreme scenarios. The EuroCORDEX-UK ensemble indicates little overall change to drought severity by 3 ◦C warming (-19 to +33%), with increases in drought intensity in some ensemble members generally offset by decreases in drought duration. By contrast, the UKCP18 Regional ensemble indicates large increases in drought severity (up to 73%), intensity and duration with only one member showing potential reductions. Both ensembles indicate increasing summer droughts, with most UKCP18 Regional ensemble members showing year-round increases in drought occurrence. Our results give context to previous studies based solely on UKCP18 Regional projections, and highlight the importance of considering climate modelling uncertainties in future drought impacts.