HYDROLOGICAL MODEL OF UKRAINE: SETUP, CALIBRATION, AND
WEB INTERFACE

The planning of river basin management should utilize a high-resolution, process-based hydrological model to tackle issues such as diffuse pollution, drought, flood forecasting, and the impact of climate change. The studies available to date only encompass five meso-scale and one large-scale river basins in Ukraine.

The objective of this study is to calibrate the Soil and Water Assessment Tool (SWAT) for all Ukrainian river basins, including upstream transboundary parts. The model could potentially assist in land management and assessing the impact of agriculture on water resources; hence, considerable attention is paid to agricultural practices and crop rotations.

The Soil and Water Assessment Tool (SWAT) is a process-based semi-distributed hydrological model developed by the United States Department of Agriculture's Agricultural Research Service (USDA-ARS) in collaboration with numerous institutions. SWAT is widely used for simulating the impact of land management practices on water resources, including water quantity and quality, as well as assessing the overall environmental impact of land use and climate changes.

The watershed, encompassing transboundary areas, covers an area of 873,600 km2, with Ukraine accounting for 68.7% of it. The inputs for the model consist of topography, river network, merged national soil maps with the properties for each soil polygon and underlying horizons, land cover, and agricultural practices such as crop rotations, fertilization, and operation schedules. In calibrating the model, we arranged daily discharge data from 56 gauges, snow cover from 61 locations, and crop yields of primary crops. The modeling period spans 41 years from 1980 to 2020. The modeling results are evaluated based on three criteria: the Nash-Sutcliffe coefficient (NS), the coefficient of determination (R2), and the percent bias (PBIAS).

The model is available via a user-friendly web platform that features an interactive map of Ukrainian subbasins. Users can inspect the model inputs for each subbasin and monitor the daily dynamics of key outputs: river discharge, water flow components, evapotranspiration, soil water, and snow cover. The results can be downloaded as an image or a CSV file for further research.

The hydrological model of Ukraine has the potential to address a wide range of issues related to water and agriculture: water supply, flood forecasting, soil water availability, water quality, the impact of climate change, and so on. The model will be expanded in the future to include sediment and nutrient transport.

Keywords: Hydrological model, Soil and Water Assessment Tool (SWAT), Ukraine river basins, river discharge, water flow.