Marie Gardelin

Development and test of the distributed HBV-96 hydrological model

Abstract A comprehensive re-evaluation of the HBV hydrological model has been carried out. The objectives were to improve its potential for making use of spatially distributed data, to make it more physically sound and to improve the model performance. The new version, HBV-96, uses subbasin division with a typical resolution of 40 km z, although any resolution can be used. In addition, each subbasin is divided into elevation bands, vegetation and snow classes. Automatic weighting of precipitation and temperature stations was introduced and a new automatic calibration scheme was developed. The modifications led to significant improvements in model performance. In seven test basins the average value of the efficiency criterion R 2 increased from 86 to 89%, with improvements in both the calibration and verification periods.

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

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.

Climate change and water resources in Sweden — analysis of uncertainties

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.