This paper presents the results of mapping the surface water transitions of the bed of the former Kakhovka Reservoir, based on Sentinel-1 radar imagery covering the period from January 2021 to May 2026 - before and after the demolition of the Kakhovka Hydroelectric Power Station dam in June 2023. The calculations are based on a methodology for classifying surface water features using a modified algorithm for the automatic extraction of water surface data from Sentinel-1 satellite images, based on the OTSU method implemented in Google Earth Engine.
The proposed approach utilizes all-weather radar data with improved spatial resolution (10 m), which is independent of cloud cover and time of day, and constructs transitions at an annual resolution for a specific territory, updated through to 2026.
The results show a sharp reduction in the area of permanent water - from approximately 1,715.1 km2 in 2021 to 204.1 km2 in 2026 - and the transformation of the bed of the former reservoir predominantly into seasonal water: the dominant type of transition in 2023 was the conversion of permanent water to seasonal water (1,474.0 km2). The accuracy of the ‘water/land’ classification was confirmed by pixel-by-pixel comparison with cloud-free Sentinel-2 imagery and by comparing areas with an independent CLMS dataset. The results obtained are suitable for monitoring Sustainable Development Goal indicator 6.6.1 and for planning the post-war restoration of water management systems in southern Ukraine.
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