ИСТИНА

The estimations of possible river Lena runoff changes near city Yakutsk (hydrological gauge Tabaga, basin area 897 000 km2) was done using runoff formation model ECOMAG (author Yu. Motovilov), based on data of global climate models projections for 21c. Further, based on the two-dimensional hydrodynamic model STREAM_2D (author V. Belikov) possible changes in the inundation with the expected changes in runoff were determined. Both runoff formation and hydrodynamic models were calibrated and validated using observed data for the historical period from 1980 year until nowadays. Runoff formation model calibrated using daily data of weather stations and reanalysis WATCH and WFDEI, has showed good correspondence of observed and simulated hydrographs, Nash - Sutcliffe criteria (NSE) for water discharges was above 0.87. Results of hydrodynamic modelling has shown good coincidence of modeled and observed daily water levels (NSE criteria for all sub-periods for water levels was above 0.90) and inundations zones. For the forecast period, runoff simulations based on the data of five global climate models, provided by the ISI-MIP2 project, have demonstrated positive mean and maximum runoff anomalies and shift of the flooding period to the earlier time. On average by the ensemble, modeling has showed an increase in the average long-term maximum water discharges from 13% under the rcp2.6 scenario to 25% under the most severe climate change scenario rcp8.5 to the middle of the 21st century. An analysis of scenario calculations based on the STREAM-2D hydrodynamic model, has showed that the expected increase in the maximum water discharges may lead to an increase in flooding area by 5-6%; the intensity of flow, which determines the risk of flooding may increase by 7% to 18% depending on the climatic scenario. The research was supported by the RFBR №18-05-60021.