Аннотация:The ECOMAG and the HYPE process-based hydrological models were setup to assess possible impacts of climate change on the hydrological regime of two pan-Arctic great drainage basins: the Lena and the Mackenzie rivers. We firstly assessed the reliability of the hydrological models to reproduce the historical streamflow series and analyzed the hydrological projections driven by the climate change scenarios. The impacts were assessed for three 30-year periods: early- (2006-2035), mid- (2036-2065) and end-century (2070-2099) using an ensemble of five GCMs and four Representative Concentration Pathways (RCP) scenarios. Results show, particularly, that the basins react with multi-year delay to changes in the RCP2.6, so-called “mitigation” scenario, and consequently to the potential mitigation measures. Then we assessed the hydrological projections’ variability, which is caused by the GCM’s and RCP’s uncertainties, and found that the variability rises with the time horizon of the projection and, generally, the prohection variability is larger for the Mackenzie than for Lena. We finally compared the potential future hydrological impacts projected based on the GCM-scenario ensemble approach and the delta-change transformation method of the historical observations. We found that the delta-change method can produce useful information about the climate change impact in these two basins, at least for the nearest decades.