Effect of a high-end CO₂-emission scenario on hydrology

In the latest IPCC report, worst case scenarios of climate change describe average global surface warming of up to 6°C from pre-industrial times by the year 2100. This study highlights the influence of a high-end 6 degree climate change on the hydrology of a catchment in central Denmark. A simulation from the global climate model, EC-Earth, is downscaled using the regional climate model HIRHAM5. A simple bias correction is applied for daily reference evapotranspiration and temperature, while distribution-based scaling is used for daily precipitation data. Both the 6 degree emission scenario and the less extreme RCP4.5 emission scenario are evaluated for the future period 2071-2099. The downscaled climate variables are applied to a fully distributed, physically based, coupled surface-subsurface hydrological model based on the MIKE SHE model code. The impacts on soil moisture dynamics and evapotranspiration show increasing drying-out tendencies for the future, most pronounced in the 6 degree scenario. Stream discharge and groundwater levels also show increased drying due to higher evapotranspiration. By comparing the 6 degree scenario with other emission scenarios, it is found that the most prominent changes in the water balance are caused by drying out of soils rather than precipitation effects.