Modelling of potential impact of climate change on water regime and channel processes in the river Lena near city Yakutsk: possibilities and limitations

STREAM_2D software package was applied for retrospective and predictive simulations of the Lena River hydraulic and channel changes during ice-free period near the city of Yakutsk. The modelling results indicate significant correspondence of simulated water discharges distribution and water levels with observed one, the model also has captured main erosion and accumulation zones, according to the 2009–2016 years observations. Runoff hydrographs of the ECOMAG runoff model simulations based on the global climate model MIROC-ESM-CHEM data were used as input for the hydrodynamic model with daily time step for two climate scenarios RCP2.6 and RCP8.5.Comparison of scenario, based on modern hydrographs, and two scenarios, based on climate projections, have shown the changes in the range of channel-forming discharges and their duration. According to the results of 20-year simulation of channel evolution for three scenarios, the position of the main areas of erosion and deposition under scenario RCP2.6 and RCP8.5 retained the same as under actual scenario, but some additional new local areas of erosion can be formed during peak flows near the banks. Erosion can increase by up to 1 - 2 meters and even more in some areas, but the shifting of some large erosion-accumulative forms is slower than according to the scenario, based on the modern hydrographs, due to the reduced duration of channel-forming flood discharges.