Modelling the impacts of climate change on upland catchments in southwest Scotland using MIKE SHE and the UKCP09 probabilistic projections

Hydrological models of three upland sub-catchments of Loch Dee, southwest Scotland, are calibrated and validated against observed discharge. Perturbed precipitation and potential evapotranspiration (PET) are generated from UKCIP09 projections for Low, Medium and High emissions scenarios for the 2050s and 2080s for probability levels between 10 and 90%. Annual and monthly PET increases for all scenarios. Central estimates of increases in annual PET are up to 10.7 (2050s) and 15.8% (2080s). Precipitation becomes more seasonal, increasing in winter and decreasing in summer for all but the extreme probability levels. Annual precipitation declines for the lowest (up to 30%) probability levels and increases thereafter (up to 5.8% for the 2050s and 10.3% for the 2080s at the 50% level). Changes in discharge are driven by those for precipitation. Although there is uncertainty in changes in annual discharge, most scenarios increase winter discharges (2050s: up to 24.2%; 2080s: up to 50.9% at the 50% level) and reduce summer flows (2050s: up to 34.2%, 2080s: up to 48.7% at the 50% level). Potential impacts include enhanced winter flooding and lower summer reservoir levels with implications for hydropower. Greater seasonality in discharge may impact fisheries and ongoing recovery from surface water acidification.