Identifying Drivers and Projecting Scenarios for Blue Water Resources in the Upper Qingjiang River Basin

Blue water is fundamental to ecological security and socioeconomic development in mountainous headwater catchments. Taking the Upper Qingjiang River Basin—a key water conservation area of the Three Gorges Reservoir—as the study area, this study develops an integrated SWAT–Geographical Detector–system dynamics framework to identify driving mechanisms and project future trends under alternative scenarios, extending previous basin studies from blue–green water scarcity to blue water volume at the township scale. Based on 2010–2022 multi-source datasets, the SWAT model provided baseline blue water estimates, the Geographical Detector quantified individual and interactive effects of ten climatic, topographic, land-use, and socioeconomic factors, and the system dynamics model simulated blue water evolution through 2030 under five scenarios. Results show that (1) natural factors dominate the spatial differentiation, with precipitation as the primary driver (mean q > 0.68) versus socioeconomic factors (max q for GDP = 0.08); (2) nonlinear enhancements prevail across factor pairs, with population–GDP interactions consistently ranking among the highest (q > 0.85 in most years); and (3) by 2030, blue water volumes rank as Ecological Conservation > Economic Prioritization > Coordinated Development > Population Growth > Baseline Development, with Ecological Conservation achieving the highest volume (471.6 million m3, 6.1% annual growth). These findings support refined water governance in Three Gorges Reservoir headwater basins.