Keywords: Average annual water runoff modules, interpolation surfaces, geographic information systems, river basins districts of Ukraine

Ukraine has adopted the principles of integrated water resources management based on the river basin approach, under which river basin districts serve as the fundamental units for water use regulation, protection, and restoration. Within this framework, the development of River Basin Management Plans (RBMPs) requires reliable hydrological characteristics of surface water bodies. In particular, data on average annual water discharge with a 50% probability of exceedance are necessary for the analysis of key RBMP components, including the assessment of pressures, impacts, and water availability at the basin scale. However, the uneven distribution of hydrological monitoring stations limits the direct application of observational data in basin-scale analyses. This study presents a geographic information system (GIS)-based approach to mapping the spatial distribution of average annual water runoff modules with a 50% probability of exceedance across the territory of Ukraine. Using modern geoinformation technologies, a digital elevation model was generated, catchment areas of hydrological gauging stations were delineated, and their centre of the catchment were determined. Based on these inputs, an interpolation surface of average annual runoff modules was constructed, enabling the automated extraction of runoff characteristics at any point within the study area. A detailed analysis of spatial variability in average annual runoff modules was performed for nine river basin districts of Ukraine. The identified spatial patterns reflect the influence of physical-geographical zonation and altitudinal differentiation, highlighting the controlling role of natural factors in runoff formation. The developed interpolation surface minimizes subjective influences inherent in traditional assessment approaches and provides an objective, reproducible tool for hydrological analysis. The results indicate that the generated interpolation surface can be effectively used in the preparation of River Basin Management Plans for all river basin districts of Ukraine, contributing to evidence-based water resources management at the national scale.

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