Climate change is likely to threaten the consistent provision of clean drinking water in the UK, in terms of both water quantity and quality. Projected increases in extreme weather events in particular, such as droughts and flooding, are likely to exacerbate both of these factors further.

Our study uses 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 quantity and quality for the Dyfi catchment in Wales, UK. We use an ensemble of 12 regionally downscaled climate models as inputs to account for uncertainty in the projections and take twenty year snapshots for 2020-40, 2040-60 and 2060-80. We focus on five specific water quality variables: stream temperature, nitrates, phosphorous, sediment load, and persistent bacteria.

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 for both water treatment measures and water security provisions.