Hydrological processes in the Norwegian Arctic for present and future climates have been estimated using available observations and hydrological modelling. A spatially distributed hydrological model has been tailored to water balance simulations in Arctic environments. The model performs water balance calculations for computational elements characterised by their elevation and land use. Each grid cell may be divided into a maximum of four land surface classes; two land use zones with different vegetations, a lake area and a glacier area. The model considers changes in glacier volume and glacier covered area. Results from atmosphere-ocean general circulation models from the Max Planck Institute, and from the Hadley Centre have been used for assessment of climate change impacts on water resources in the Norwegian Arctic. The results show that annual runoff for the Norwegian Arctic will increase. Seasonal runoff changes vary, with increase in winter and decrease during spring and summer. Autumn runoff will generally increase. Runoff changes are strongly linked to changes in snow regime and glacier mass balance. Snow cover will be more unstable and all scenarios indicate increase in winter and autumn runoff in areas where the snow cover has a major impact on runoff in the control climate. Glacier mass balance will be negative in the future, resulting in a large melt water contribution during the period of melt down of glaciers. Uncertainty of model simulations have been assessed using results from multiple hydrological model parameter sets, emission scenarios for greenhouse gases and atmospheric model results.