Modeling of maximum runoff characteristics of small rivers in the mountain permafrost zone

Climate change leads to the transformation of hydrological processes in the mountain permafrost regions, increasing the frequency and intensity of catastrophic floods. An example is the Magadan Oblast — an important region for the Russian economy, exposed to the risk of floods. The aim of the study was to calculate the maximum water discharge of three small rivers in the Magadan Oblast — the Krivulya, Ambardakh and Susuman rivers — using pluviograph data and the hydrological model Hydrograph. The model was verified on daily intervals for the periods 1966–1994 for the Krivulya stream and 1966-1987 for the Susuman and Ambardakh rivers. Modelling results have shown satisfactory correlation with the observed daily and mean annual values. The median values of the Nash-Sutcliffe coefficient varied from 0.52 to 0.62. The model parametrization for three main types of the landscapes was developed based on the data of the Kolyma Water-Balance station. The modeling was carried out for the historical floods of August 16, 1986 for the Susuman and Ambardakh rivers (maximum observed instant discharges were 393 m3/s and 74.7 m3/s, calculated 1-hourly discharge — 420 m3/s and 78.5 m3/s, respectively) and July 26, 1984 for the Krivulya Stream (observed instant discharge — 14.2 m3/s, calculated 1-hourly discharge — 16.5 m3/s). The relative error of simulated and observed maximum discharges did not exceed 20%. The results of the study confirm the possibility of applying deterministic hydrological modeling on an intra-day interval using pluviograph data. However, the main limitation for the mountain cryolithozone remains the lack of precipitation data. A promising solution may be the use of climate model data, which, in combination with runoff formation models, opens up new opportunities for assessing and predicting maximum runoff characteristics.