Post-Breach Landscape Transformation of the Former Kakhovka Reservoir Bed

Abstract

Abstract The destruction of the Kakhovka Hydropower Plant dam in June 2023 caused rapid drainage of one of the largest reservoirs in Ukraine and exposed an extensive reservoir bed that began to develop as a new post-disturbance landscape mosaic. This study assesses the post-breach landscape transformation of the former Kakhovka Reservoir bed using multi-temporal Sentinel-2 and Landsat 8/9 satellite data processed in Google Earth Engine. The analysis combines a five-class surface-type classification, monthly structural dynamics, transition-matrix analysis for 2023–2025, an author-proposed Degradation State Difference Index (DSDI), and statistical evaluation of vegetation-moisture-temperature relationships. Five surface types were identified: residual water bodies, dry sandy-detrital surfaces, flat dry muddy surfaces, wet or waterlogged surfaces, and surfaces with a distinct vegetation signal. Between 19 August 2023 and 19 August 2025, the area of residual water decreased from 312.7 km² to 136.2 km², while surfaces with a distinct vegetation signal increased from 265.4 km² to 1315.7 km². The dominant transition pathway was the conversion of flat dry muddy surfaces to surfaces with a distinct vegetation signal, covering 540.7 km². DSDI indicated a substantial reduction in highly degraded surfaces, with DSDI ≥ 0.50 decreasing from 1067.7 km² in summer 2023 to 127.9 km² in summer 2025. Nevertheless, large areas remained exposed to residual thermal and moisture stress. In 2025, Spearman correlations between NDVI and NDMI, NDVI and LST, and NDMI and LST were 0.89, -0.64, and -0.71, respectively. The DSDI-NDMI relationship also showed a strong negative association (Spearman ρ = -0.94), indicating that the integrated degradation signal decreased with increasing surface moisture. The results show that the former reservoir bed should not be interpreted only as a degraded surface, but as a rapidly reorganising post-reservoir landscape mosaic combining initial vegetation establishment, potential surface stabilisation and persistent ecological risks.