In recent years, rain floods caused by abnormal rainfall precipitation have caused several damages in various part of Russia. Precise forecasting of rainfall runoff is essential for both operational practice to optimize the operation of the infrastructure in urbanized territories and for better practices on flood prevention, protection, and mitigation. The network of rain gauges in some Russian regions are very scarce. Thus, an adequate assessment and modeling of precipitation patterns and its spatial distribution is always impossible. In this case, radar data could be efficiently used for modeling of rain floods, which were shown by previous research. This study is aimed to simulate the rain floods in the small catchment in north-west Russia using radar- and ground-based measurements. The investigation area is located the Polomet’ river basin, which is the key object for runoff and water discharge monitoring in Valdai Hills, Russia. Two datasets (rain gauge and weather radar) for precipitation were used in this work. The modeling was performed in open-source Soil and Water Assessment Tool (SWAT) hydrological model with three types of input data: rain gauge, radar, and gauge-adjusted radar data. The simulation efficiency is assessed using the coefficient of determination R2, Nash–Sutcliffe model efficiency coefficient (NSE), by comparing the mean values to standard deviations for the calculated and measured values of water discharge. The SWAT model captures well the different phases of the water regime and demonstrates a good quality of reproduction of the hydrographs of the river runoff of the Polomet’ river. In general, the best model performance was observed for rain gauge data (NSE is up to 0.70 in the Polomet’river-Lychkovo station); however, good results have been also obtained when using adjusted data. The discrepancies between observed and simulated water flows in the model might be explained by the scarce network of meteorological stations in the area of studied basin, which does not allow for a more accurate correction of the radar data.

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<p>The previous research had shown that change of rainfall structure is taking place over Russia which increases the probability of occurrence of hazardous hydrological phenomena such as flash rainfall floods. Thus, the relevance and significance of the study is determined by the necessity of taking into account the structural changes of precipitation for reliable estimates of rainfall runoff characteristics in terms of climate change. The data of this study are comprehensive and consist of various sources of hydrometeorological information, including ground-based observations of precipitation and runoff, radar data. The assessment of the changes occurred in the maximum rainfall runoff and daily rainfall depth within the Russian part of the Baltic Sea basin was carried out in this study. The majority of the basins in our study showed positive trends in maximum discharge. The results of the work describe the experience of using different types of meteorological information of precipitation for rainfall floods modeling. The open-source SWAT (Soil and Water Assessment Tool) hydrological model was utilized. Small catchment (631 km<sup>2</sup>) situated in the Polomet’ River basin were chosen as the object of test modeling. The simulation efficiency is assessed using the coefficient of determination R<sup>2</sup>, Nash–Sutcliffe model efficiency coefficient (NSE), by comparing the mean values to standard deviations for the calculated and measured values of water discharge. This study was supported by RFBR, grant 19-35-90123 “Rain floods in the North-West Russia: assessment of variability and development of new forecasting methods”.</p>

The flood monitoring carried out by Roshydromet is aimed at preventing (forecasting) and alerting the achievement of critical (hazardous) water levels in water bodies to reduce the negative effect of floods. Based on long-term observations at Roshydromet gaging stations on the Northwestern Federal District rivers with established critical water levels at which an inundation of coastal territories occurs, the hazard category is determined for the past river floods, and their quantification is provided. Gaging stations with a high frequency of exceeding hazardous water levels leading to a partial flooding of settlements and economic facilities are identified. The main reason for flooding in these cases was the use of riverside areas without considering peculiarities of the water regime of rivers.