<![CDATA[Urbanisation and land-use conversion in tropical urban watersheds have increasingly contributed to ecological degradation and hydrological instability, particularly through the reduction of vegetation cover and the expansion of impervious surfaces. This study aimed to analyse the spatial dynamics of vegetation cover using the Normalised Difference Vegetation Index (NDVI) and to evaluate its implications for hydrological changes in the Wae Batu Merah Watershed, Ambon City, Indonesia, during the period 2013–2024. A quantitative spatial–hydrological approach was employed by integrating remote sensing analysis, Geographic Information Systems (GIS), and hydrological interpretation. Satellite imagery from Landsat and Sentinel platforms was processed to generate NDVI classifications, while hydrological data were used to assess changes in peak discharge. The results revealed a substantial decline in vegetation quality and watershed ecological function over the observation period. The average NDVI value in the upstream watershed decreased from 0.46 in 2013 to 0.28 in 2023, representing a decline of 39.13%. Simultaneously, buffer vegetation area decreased by 42%, whereas built-up and settlement areas increased by 84%. Spatial analysis demonstrated that areas classified as high greenness and medium greenish became increasingly fragmented, while low greenness, very low greenness, and non-vegetation classes expanded significantly, particularly in the western and transitional watershed zones. These land-cover changes were accompanied by an increase in peak discharge from 58.0 m³/s to 69.8 m³/s, indicating intensified surface runoff and reduced infiltration capacity. The findings confirm a strong ecological–hydrological relationship between vegetation degradation and watershed response in tropical small-island urban catchments. This study highlights the effectiveness of NDVI as a spatial indicator for watershed health assessment and provides scientific evidence to support vegetation-based watershed conservation, ecological restoration, and sustainable urban land-use planning.]]>
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