Vegetation Loss and Incomplete Recovery Associated with Repeated Glacier-Related Hazards at the Sedongpu Valley Outlet, China, 2015–2025

The Sedongpu Valley has experienced repeated ice–rock avalanches, glacier detachments, and related hazards, but the long-term vegetation trajectory in this hazard-affected outlet landscape remains poorly documented. To document vegetation changes in relation to the published hazard sequence, quality-controlled Landsat and Sentinel-2 observations from 2015 to 2025 were used to reconstruct annual NDVI, EVI, and SAVI for a 3.41 km2 outlet analysis grid. Published hazard and elevation-change studies and ERA5-Land data provided environmental context. The largest observed annual decline occurred during 2017–2018: median NDVI decreased from 0.845 to 0.688, while low-NDVI area increased from 0.05 to 0.82 km2. Among 977 fixed pixels that crossed from NDVI ≥ 0.30 in 2017 to <0.30 in 2018, 25.8% were again at or above the threshold in 2025, following a non-monotonic annual trajectory. Alternative thresholds of 0.25 and 0.35 gave endpoint proportions of 25.4% and 25.9%. Mean paired-pixel NDVI change over 2015–2025 remained −0.137. The July 2017 acquisition introduces seasonal uncertainty, and concurrent climate correlations do not isolate causal effects. The results document spatially uneven, incomplete spectral recovery within a landscape affected by repeated glacier-related hazards and subsequent geomorphic reworking.