The Effect of Natural and Anthropogenic Climate Changes on River Runoff and Snow Water Equivalent in the Lena River Basin

The hydrological models ECOMAG and HBV were used to calculate the characteristics of river flow and snow Water Equivalent in the Lena River basin. The input data included the meteorological observations and the results of calculations with global climate models with the implementation of scenarios of natural climate conditions, taking into account the anthropogenic effect on climate. The calculations were made for a historical period (1970–1999) and up to the end of the XXI century. Hydrological models for several hydrometric gages in the Lena basin were calibrated and verified. The simulation of the annual and seasonal runoff using the climate model data was evaluated by comparison with observation data. According to the results using numerical experiments over the historical period, the increase in the Lena runoff is mostly due to natural climate variations. Conversely, in the XXI century, the anthropogenic climate changes determine the specific features of the regime of river runoff and snow cover. The warming caused by an increase in greenhouse gas concentrations in the atmosphere leads to an increase in snow water equivalent and transformation of the hydrological regime in the area, in particular, to an earlier beginning of active snow melting (up to two weeks) and higher maximal discharges during spring flood. At the same time, the volume of runoff decreases in the summer and increases in the autumn and winter.