Modelling Climate Change Impacts on Water Resources in the Swedish Regional Climate Modelling Programme

Abstract

The Swedish Regional Climate Modelling Programme (SWECLIM) focuses on interpretation of climate scenarios for the Nordic Region. Water resources studies include hydrological model simulations both at the large scale to simulate trends for the entire Baltic Basin and at smaller basin scales to simulate local impacts in Sweden. Global climate model simulations (GCMs) provide lateral boundary conditions to drive the finer resolution Rossby Centre regional atmospheric climate model (RCA) in dynamical downscaling. Two different GCMs-HadCM2 and ECHAM4/OPYC3-have thus far been used. Analyses of future climates are created from differences in 10-year time slices between RCA control runs of the present climate and RCA scenario climate runs with transient greenhouse gas simulations. These differences drive the offline hydrological impacts assessment models. Both of the RCA climate scenarios show overall increases in temperature and precipitation for the Nordic Region, although spatial and temporal distribution varies between them. Hydrological model scenario simulations show a strong decrease in snowmelt peak river discharge. Modelled changes to average annual freshwater inflow to the Baltic Sea vary from +8% to -21% from present day conditions. The interface between atmospheric models and hydrological impact models is a weak link in the process, as is representation of evapotranspiration in the hydrological models for a future climate.