Monitoring Mangrove Dynamics Using Remote Sensing in the Welu and Chanthaburi Estuaries, Chanthaburi, Thailand

Mangrove forests play a crucial role in coastal environments by providing ecosystem services, supporting biodiversity, and contributing to nature-based solutions for climate change mitigation and adaptation. This study investigated spatio-temporal changes in mangrove extent and assessed mangrove canopy condition in the Welu and Chanthaburi Estuaries, Chanthaburi Province, Thailand, using Sentinel-2 Level-2A imagery gathered from 2015 to 2024. Mangrove extent was extracted using the mangrove vegetation index (MVI). Mangrove canopy condition was assessed through two key dimensions: mangrove greenness and mangrove forest density. Greenness was evaluated using the chlorophyll vegetation index (CVI), normalized difference moisture index (NDMI), and normalized difference chlorophyll index (NDCI). Density was assessed using the optimized soil-adjusted vegetation index (OSAVI) and the renormalized difference vegetation index (RDVI). These indices were integrated using the entropy weight method to construct composite mangrove condition indices, and their accuracy was assessed using a confusion matrix based on validation points, Google Earth historical imagery, and field survey observations. The MVI-based extraction achieved high accuracy, ranging from 93% to 95% for the Welu Estuary and 94% to 96% for the Chanthaburi Estuary, with Kappa coefficients ranging from 0.81 to 0.85 in both cases. The Welu Estuary showed an increasing mangrove extent, from approximately 91.4 km2 in 2015 to 103.9 km2 in 2024; over the same period, in the Chanthaburi Estuary, it increased slightly from 29.9 km2 to 31.7 km2. The mangrove canopy assessment results indicated that both estuaries were generally dominated by moderate-to-high canopy density and greenness. However, the Chanthaburi Estuary exhibited greater spatial heterogeneity and higher fragmentation, particularly near aquaculture areas and pond margins, whereas the Welu Estuary maintained more continuous and structurally stable mangrove patches. These findings demonstrate that integrating Sentinel-2-derived MVI, composite vegetation indices, and spatial interpretation provides an effective framework for long-term mangrove monitoring and supports restoration planning, coastal resource management, and nature-based solutions.