Assessing Riparian Vegetation Dynamics and Resilience Under Climate Change Using Sentinel-2 and LiDAR: A Case Study of the Duero River Basin, Spain

Riparian ecosystems are critical regulators of hydrological and biogeochemical cycles, yet face accelerating degradation under Mediterranean drought regimes and rising water-extraction pressure. This study integrates eight years of Sentinel-2 multispectral time series (2017–2024) with airborne LiDAR structural data (PNOA) to assess riparian vegetation vulnerability across six critical areas in the Duero River Basin, northwestern Spain. Five spectral indices (NDVI, NDMI, MSI, EVI, and NMDI) were analyzed alongside LiDAR-derived canopy structural metrics, particularly the proportion of high canopy cover ($P_{\mathrm{HIGH}}>15$ m). Results reveal pronounced spatial heterogeneity in functional trajectories. Bernesga, a site with relatively high canopy structure ($P_{\mathrm{HIGH}}=26\%$), showed significant declines in all five indices (NDVI: $-0.0158$ yr⁻¹), whereas the remaining sites showed positive NDVI slopes, significant only at Arlanza. Trend slopes were not significantly related to the proportion of high canopy cover ($P_{\mathrm{HIGH}}$ 2–62%; NDVI: $R^2=0.04$, $p=0.711$). Moisture-sensitive indices (NDMI, NMDI) and stress-related indices (MSI, EVI) showed coherent responses during documented dry years (2017, 2019, 2022), suggesting that multi-index spectral monitoring can detect climate-related vegetation responses that may precede detectable differences in canopy structure. The proposed Sentinel-2 and LiDAR integration framework provides an integrated approach for assessing riparian vegetation functional stability and supporting the preliminary screening of riparian sites for field assessment across Mediterranean river networks under increasing drought pressure.