Antagonistic Roles of Climate Change and Human Activities in Reshaping Yangtze River Turbidity Revealed by a Virtual Satellite Constellation

The Yangtze River, one of the world’s largest river systems, plays a vital role in regional ecological security. However, monitoring its turbidity dynamics remains difficult. Most satellite-based algorithms are designed for lakes or estuaries and often fail in narrow, optically complex rivers. Moreover, the temporal resolution constraints of individual satellites are insufficient to resolve the rapid short-term variability in rivers (e.g., 8 days for Landsat-8/9). To address these challenges, we developed a virtual satellite constellation by integrating Landsat-8/9 and Sentinel-2 imagery (2013 to 2023), reconstructing a high-resolution turbidity dataset for the Yangtze River. We built sensor-specific support vector regression models ( R 2 = 0.74 and 0.66 and root mean square error [RMSE] = 16.62 and 17.74 Nephelometric Turbidity Units (NTU) for Sentinel-2 and Landsat-8/9, respectively), which outperformed other algorithms. An empirical cross-sensor harmonization method further reduced inter-mission biases (RMSE = 15.45 ± 13.43 NTU; symmetric mean absolute percentage error = 12.53% ± 15.98%). This constellation improved temporal resolution from 5 to 16 days to 2.5 days on average. The reconstructed dataset revealed a mean turbidity of 67.75 ± 58.35 NTU, with significant seasonal (wet > dry) and spatial patterns (reaches on the Qinghai–Xizang Plateau > mid-lower reaches > cascade reservoirs). Over the past decade, trends diverged sharply: turbidity increased in reaches on the Qinghai–Xizang Plateau (8.12 ± 5.51 NTU year −1 ) due to climate-induced warming and enhanced runoff accelerating erosion, but declined in cascade reservoirs (−3.40 ± 3.17 NTU year −1 ) and mid-lower reaches (−2.06 ± 1.04 NTU year −1 ) because of sediment trapping and ecological restoration. This study establishes a framework for high-frequency river water quality monitoring and highlights the antagonistic effects of climate change and human activity on sediment dynamics.