The Impact of Climate Change upon the Snowmelt Hydrology of an Upland UK Catchment

Abstract

Snowmelt hydrology is important in the winter flow regime of upland catchments in the UK as it can attenuate the extremes of the river flow hydrograph. The sensitivity of snow accumulation and melt to changes in climate, in particular to increases in temperature, could impact upon the variability of the winter flow regime. The potential impacts of this change are increases in flood risk and decreases in low flows. Hence this project investigated the consequences of projected climatic change upon snowmelt hydrology of the Dacre Beck catchment in the English Lake District. A distributed snowmelt model was created which spatialised temperature and precipitation data across the catchment. The model accumulated snow when the temperature fell below 0°C and applied one of three temperature-index snowmelt equations to melt the accumulated snowpack. The model was driven using stochastic baseline and projected (2050s medium emissions) weather series calculated using the UKCP09 weather generator. The results showed a large future reduction in both winter snow accumulation and the magnitude of snowmelt hydrology. However, the limited hydrological process representation of the model meant it could not reliably forecast changes in the winter flow regime. Therefore the snow accumulation and melt equations were incorporated into the physically based Connectivity Runoff Model (CRUM). This improved model was calibrated to observed discharge data within a Generalised Likelihood Uncertainty Estimation (GLUE) framework before being run with a sample of baseline and projected UKCP09 weather generator series. The results showed that both high and low flows in the winter flow regime were likely to increase which contradicted previous expectations but it was unclear about the role of snowmelt hydrology in these changes. Further investigation using temperature perturbed weather series found that these changes in the winter flow regime were most likely caused by increases in rainfall which overrode the impact of changes in snowmelt hydrology.