RAIN FLOODS IN THE DETRIN RIVER BASIN (MAGADAN REGION): ANALYSIS OF THE FORMATION CONDITIONS AND MODELING

Abstract

Statistics for the Magadan Region show that catastrophic floods occur in the region every year, and the damage from them is estimated at hundreds of millions of rubles. There is no system for short-term forecasting hazardous hydrological phenomena in the region. The study aims to analyze the main factors in the formation of catastrophic rain floods in the Ust-Omchug village, as well as to assess the possibility of using the Hydrograf distributed hydrological model to develop a system for short-term forecasting of river flow in the Magadan Region using the example of the Detrin River basin. The impact of climate change on runoff formation is examined based on the hydrometeorological observation data from the Roshydromet network. Since 1967, precipitation in the region has increased by 16 %, with the largest increase observed in August and September. The forecast of changes in precipitation for 2041–2060 compared to the period 1981–2010, based on climate models, has shown that an increase in annual precipitation of 10–15 % or more is expected, as well as an increase in annual river runoff of 30 % or more. To assess the applicability of the Hydrograf hydrological model as the basis for a short-term flood forecasting system for Ust-Omchug, we carried out parameterization and verification of the model on the basis of historical data. The results of modeling based on a daily simulated time interval for the period 1966–2024 were accepted as satisfactory. The WRF numerical weather prediction model with a spatial resolution of 3 km and a lead time of 3–6 hours to 1 day was used to reproduce the catastrophic floods of 2013 and 2019. The WRF model significantly overestimates the amount of solid precipitation, while in the warm period it underestimates the amount of liquid precipitation despite the satisfactory reproduction of its timing. Uneven precipitation in mountainous conditions and a sparse network of meteorological stations reduce the timing and accuracy of forecasting hazardous hydrological phenomena. In order to improve the reliability of the forecasting system and to take into account the diversity of weather conditions, it is necessary to apply an ensemble approach based on the use of input data from a variety of hydrometeorological models. The scientific novelty of the study lies in complex application of hydrological modeling and a numerical weather prediction model for flood assessment in poorly studied river basins of the mountain cryolithozone.