Decadal dynamics of surface water extent and quality in Fujian Province, China: An integrated optical-SAR remote sensing analysis using Landsat and Sentinel-1 time series (2015–2024)
- 1School of Geographical Sciences, School of Carbon Neutrality Future Technology, Fujian Normal University, Fuzhou 350117, China; College of Environmental and Resource Sciences, College of Carbon Neutral Modern Industry, Fujian Normal University, Fuzhou 350007, China; Fujian Key Laboratory of Pollution Control and Resource Reuse, Fuzhou 350007, China
- 2College of Geographical Sciences, Faculty of Geographical Science and Engineering, Henan University, Zhengzhou 450046, China
- 3College of Environmental and Resource Sciences, College of Carbon Neutral Modern Industry, Fujian Normal University, Fuzhou 350007, China
Abstract
Surface water resources are essential for ecosystem services, human welfare and climate regulation, yet face increasing pressure from climate variability and human activity. This study examined surface water extent, relative water-quality proxies and thermal regulation in Fujian Province, China, during 2015–2024 using Landsat 8/9 and Sentinel-1 SAR. Optical water was mapped with a majority-voting ensemble of NDWI, MNDWI and AWEI (threshold >0) and fused with Sentinel-1 detections constrained by MNDWI > −0.15. A − 0.85 dB shift in Sentinel-1 VV backscatter between 2015 and 2016, coinciding with the start of Sentinel-1B acquisitions, was identified; it produced a spurious +577 km 2 increase in SAR-only water area, so SAR was used only as an MNDWI-constrained complement to the optical mask. Against the JRC Global Surface Water occurrence layer (>80%), used as a Landsat-derived consistency benchmark, the optical ensemble achieved F1 = 0.70, Kappa = 0.70 and IoU = 0.54. Fused water area ranged from 1476.76 to 1729.26 km 2 (mean 1573.95 km 2 , 1.27% of the land area). After a two-year persistence filter, net change was −106.63 ± 32.80 km 2 in 2015–2020, +65.05 ± 23.40 km 2 in 2020–2024 and − 41.58 ± 35.72 km 2 over the decade. On pixels that were water in all ten years, turbidity and total suspended matter proxies declined by 5.64% and 15.84% (Mann–Kendall p < 0.05), whereas the CDOM proxy showed no significant trend. In summer, water bodies were 2.45 ± 0.44 °C cooler than land within 1 km and 1.60 ± 0.52 °C cooler than land within 2 km ( p < 0.001), whereas a province-wide comparison reversed the sign because of elevation effects. These results provide a baseline for water-resource management and heat mitigation in rapidly developing coastal regions.
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BibTeX
@article{ahamad2026decadal,
title = {{Decadal dynamics of surface water extent and quality in Fujian Province, China: An integrated optical-SAR remote sensing analysis using Landsat and Sentinel-1 time series (2015–2024)}},
author = {Muhammad Irfan Ahamad and Yuping Su and Zabih Ullah and Jehangir Ijaz and Sheraz Akhtar Gil and Zhou Yuanyuan},
journal = {Ecological Indicators},
year = {2026},
month = oct,
doi = {10.1016/j.ecolind.2026.115744},
url = {https://doi.org/10.1016/j.ecolind.2026.115744},
note = {CC BY},
}
RIS
TY - JOUR
TI - Decadal dynamics of surface water extent and quality in Fujian Province, China: An integrated optical-SAR remote sensing analysis using Landsat and Sentinel-1 time series (2015–2024)
AU - Muhammad Irfan Ahamad
AU - Yuping Su
AU - Zabih Ullah
AU - Jehangir Ijaz
AU - Sheraz Akhtar Gil
AU - Zhou Yuanyuan
PY - 2026
DA - 2026/10/30
JO - Ecological Indicators
DO - 10.1016/j.ecolind.2026.115744
UR - https://doi.org/10.1016/j.ecolind.2026.115744
AB - Surface water resources are essential for ecosystem services, human welfare and climate regulation, yet face increasing pressure from climate variability and human activity. This study examined surface water extent, relative water-quality proxies and thermal regulation in Fujian Province, China, during 2015–2024 using Landsat 8/9 and Sentinel-1 SAR. Optical water was mapped with a majority-voting ensemble of NDWI, MNDWI and AWEI (threshold >0) and fused with Sentinel-1 detections constrained by MNDWI > −0.15. A − 0.85 dB shift in Sentinel-1 VV backscatter between 2015 and 2016, coinciding with the start of Sentinel-1B acquisitions, was identified; it produced a spurious +577 km 2 increase in SAR-only water area, so SAR was used only as an MNDWI-constrained complement to the optical mask. Against the JRC Global Surface Water occurrence layer (>80%), used as a Landsat-derived consistency benchmark, the optical ensemble achieved F1 = 0.70, Kappa = 0.70 and IoU = 0.54. Fused water area ranged from 1476.76 to 1729.26 km 2 (mean 1573.95 km 2 , 1.27% of the land area). After a two-year persistence filter, net change was −106.63 ± 32.80 km 2 in 2015–2020, +65.05 ± 23.40 km 2 in 2020–2024 and − 41.58 ± 35.72 km 2 over the decade. On pixels that were water in all ten years, turbidity and total suspended matter proxies declined by 5.64% and 15.84% (Mann–Kendall p < 0.05), whereas the CDOM proxy showed no significant trend. In summer, water bodies were 2.45 ± 0.44 °C cooler than land within 1 km and 1.60 ± 0.52 °C cooler than land within 2 km ( p < 0.001), whereas a province-wide comparison reversed the sign because of elevation effects. These results provide a baseline for water-resource management and heat mitigation in rapidly developing coastal regions.
SN - 1470-160X
SN - 1872-7034
ER -