A remote sensing–based assessment of long-term vegetation dynamics following dam construction in a Mediterranean watershed (Cyprus)

Abstract On Mediterranean intermittent rivers, dams reorganise downstream flow regimes and the shallow groundwater that sustains riparian vegetation. Where no environmental-flow requirement applies and no flood pulses are programmed, disentangling dam-driven vegetation change from background climate variability requires a robust multi-decadal spectral record combined with spatially explicit attribution diagnostics. This study presents a 40-year (1984–2024) Landsat Enhanced Vegetation Index (EVI) time series for the downstream riparian corridor of the Klirou–Malounta–Akaki Dam (central Cyprus; Akaki/Serrachis River; commissioned 2007), constructed by cross-sensor harmonisation of Landsat 5 TM, Landsat 7 ETM + and Landsat 8 OLI Collection 2 Surface Reflectance products using a Random Forest calibration pipeline in Google Earth Engine and R. Hydroclimatic controls were assessed using Mann–Kendall trend tests and Wilcoxon rank-sum tests on precipitation records from two local gauges; no significant long-term trend (τ = − 0.003, p = 0.566) and no significant pre- to post-dam precipitation shift ( p = 0.061) were detected. Five-year step-change mapping combined with pixel-wise Wilcoxon level-shift, Pettitt change-point and Mann–Kendall trend attribution, applied under false discovery rate control, identifies a coherent, delayed greening response confined to a ~ 400 m right-bank riparian corridor, where the most responsive pixels show EVI gains of 75–92% relative to the pre-dam baseline, with the strongest signal concentrated in the 2011–2015 period, a lag of approximately four years consistent with post-impoundment groundwater stabilisation. Field validation at four sites confirms species composition dominated by non-native Eucalyptus spp. and phreatophytic understory expanding under reduced flood disturbance and stabilised shallow moisture. These findings demonstrate that spectral greening in a regulated Mediterranean corridor reflects ecological conditions that can inform environmental-flow policy and riparian restoration planning. The study provides a transferable template for dam-impact monitoring across the Mediterranean Basin and other semi-arid regions where long-term riparian vegetation records remain absent.