Hydrological and ecological consequences of the Kakhovka dam collapse

Abstract The destruction of the Kakhovka dam in June 2023 represents one of the most severe environmental consequences of the Russo-Ukrainian war, transforming a regulated reservoir into a dynamic fluvial landscape and disrupting hydrological processes at basin scale. Using a multi-sensor remote sensing approach-including Gravity Recovery and Climate Experiment Follow-On gravimetry, Sentinel-1 and Sentinel-2 imagery, satellite altimetry (Database for Hydrological Time Series over Inland Waters, Surface Water and Ocean Topography), and causal inference modeling-we assess the cascading impacts on total water storage anomaly (TWSA), river hydrodynamics, flooding, and vegetation dynamics. A Bayesian structural time series (BSTS) analysis reveals that the time-integrated TWSA deviation relative to the counterfactual decreased <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>83</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>cm</mml:mtext> <mml:mo>±</mml:mo> <mml:mn>36</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>cm</mml:mtext> <mml:mstyle scriptlevel="0"/> <mml:mo stretchy="false">(</mml:mo> <mml:mn>90</mml:mn> <mml:mi mathvariant="normal">%</mml:mi> <mml:mstyle scriptlevel="0"/> <mml:mtext>CI</mml:mtext> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> </mml:math> by June 2025. This loss reflects immediate surface water depletion and ongoing groundwater drainage into the emptied reservoir, with field evidence confirming groundwater storage decline. The collapse further amplified hydrological variability in the Dnieper River, with downstream water surface elevation fluctuations nearly doubling relative to the pre-collapse regime. Flooding patterns reveal episodic inundation, peaking at 900 km 2 in March 2024 before contracting below 300 km 2 , while wetlands re-emerged in drained areas but face long-term sustainability challenges due to falling groundwater levels. More broadly, our findings demonstrate how armed conflict can trigger compounded hydrological disruptions, advancing causal analysis of TWS with BSTS in a novel framework and exposing the unprecedented severity of groundwater losses alongside surface water change.