Climate change impact on the water regime of two great Arctic rivers: modeling and uncertainty issues Alexander Gelfan 1,2 & David Gustafsson 3 & Yury Motovilov 1,2 & Berit Arheimer 3 & Andrey Kalugin 1,2 & Inna Krylenko 1,4 & Alexander Lavrenov 1 Received: 30 November 2015 /Accepted: 20 May 2016 # Springer Science+Business Media Dordrecht 2016 Abstract The ECOlogical Model for Applied Geophysics (ECOMAG) and the HYdrological Predictions for the Environment (HYPE) process-based hydrological models were set up to assess possible impacts of climate change on the hydrological regime of two pan-Arctic great drainage basins of the Lena and the Mackenzie Rivers. We firstly assessed the reliability of the hydrological models to reproduce the historical streamflow series and analyzed the hydrolog- ical 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 global climate models (GCMs) and four Representative Concentration Pathway (RCP) scenarios. Results show, particularly, that the basins react with a multi-year delay to changes in RCP2.6, so-called Bmitigation^ 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 projection variability is larger for the Mackenzie than for the Lena. We finally compared the mean annual runoff anomalies projected under the GCM-based data for the twenty-first century with the corresponding Climatic Change DOI 10.1007/s10584-016-1710-5 This article is part of a Special Issue on BHydrological Model Intercomparison for Climate Impact Assessment^ edited by Valentina Krysanova and Fred Hattermann Electronic supplementary material The online version of this article (doi:10.1007/s10584-016-1710-5) contains supplementary material, which is available to authorized users. * Alexander Gelfan hydrowpi@mail.ru 1 Water Problems Institute of RAS, Moscow, Russia 2 P.P. Shirshov Institute of Oceanology of RAS, Moscow, Russia 3 Swedish Meteorological and Hydrological Institute, Norrköping, Sweden 4 Lomonosov Moscow State University, Faculty of Geography, Moscow, Russia