Climate change is likely to threaten the consistent provision of clean drinking water in the UK, in terms of both water quantity and quality. Water quality could be especially problematic due to projected increases in extreme weather events such as droughts and flooding, both of which have a deleterious impact on water quality.

Our study uses the Soil and Water Assessment Tool (SWAT) with UK Climate Projections 2018 data to model the impacts of a worst case scenario in terms of global emissions (RCP8.5), on water quality for five catchments in Wales, UK. We use an ensemble of 12 regionally downscaled climate models as inputs to account for uncertainty in the projections and take snapshots for the 2030s, 50s and 80s. We focus on five specific water quality variables: stream temperature, nitrates, phosphorous, sediment load, and persistent bacteria.

At all five study catchments, SWAT is calibrated using river flow data only, due to the lack of water quality measurements. SWAT parameters related to water quality are kept at their default values. While our approach increases the uncertainty related to the specific values of water quality variables, it does provide the relative changes in specific water quality variables under future climate conditions. This information would still be useful for water resource management planning, especially in terms of the potential adaptation measures required to cope with the additional treatment required at water treatment works. By taking snapshots our study also allows for short, medium and long term solutions to be planned.