Modelling and statistical analysis of catchment water balance and discharge in Finland in 1951–2099 using transient climate scenarios

In this study climate change impacts on water balance components were estimated from transient climate scenarios for 1951–2099 in Finland. The future changes in evapotranspiration and discharge in annual and seasonal scales as well as annual mean high and low flows were projected for four catchments in different parts of Finland. The assessment was carried out using temperature and precipitation series simulated by four regional climate models (RCMs) as input to a conceptual hydrological model. The daily data from RCMs was bias corrected with the quantile–quantile mapping method and statistical properties of the simulated discharges were analysed to detect trends over time. Without bias correction the simulated discharges in the control period did not match the observed discharges, but the fit was improved considerably after bias correction. The results showed that seasonal changes, most importantly increase in winter runoff, were clearly visible and consistent in different climate scenarios and catchments. Individual scenarios also produced changes in annual mean, high and low flows, but without consistency in scenarios. The use of bias corrected RCM data as input to the hydrological model enables transient simulations, but the simulation results aggregate considerable uncertainties from the climate modelling, bias correction and the hydrological model.