Climate change and water resources in Sweden — analysis of uncertainties

Abstract

Simulations of the impacts of climate change on water resources in Sweden are produced within the Swedish Regional Climate Modelling Programme, SWECLIM. The impact studies are based on a combination of global climate models (GCMs), a regional climate model and a hydrological runoff model. The two different GCMs used so far are the UKMO HadCM2 from the Hadley Centre and the ECHAM4/OPYC3 of the Max Planck Institute for Meteorology. The regional climate model, RCA, was developed at the Rossby Centre of the Swedish Meteorological and Hydrological Institute (SMHI) and is a modified version of the international HIRLAM meteorological forecast model. The RCA model performs downscaling from GCM scenarios on a time horizon of 50 to 100 years. Based on the RCA scenarios, water resources scenarios were produced with the HBV hydrological runoff model developed at the SMHI. Two different methods for estimation of evapotranspiration in the hydrological model were used. Neither of the methods takes into account the possible feedback from changing land-use, vegetation dynamics or changing plant use of water at increasing CO2 concentrations in the atmosphere. The impacts on water resources were simulated from differences between control runs and scenario runs of the RCA model for a number of selected test basins covering the major climate regions in Sweden. Changes in runoff totals, runoff regimes and extreme values were analysed with focus on the uncertainties introduced by the choice of global climate model, routines for estimation of evapotranspiration in the hydrological model and methods applied in the interface between the models. It was further analysed how these choices affect the statistical return periods of future extremes in a design situation.