Pollution-driven surface water quality improvement and expanding population benefits in karst regions of China

Karst regions in China have high geological permeability, fragmented river networks, and strong surface–groundwater interactions, making water quality management challenging. Despite their ecological and societal importance, long-term patterns of surface water quality remain poorly understood. Here we provide a nationwide, multi-decadal evaluation of surface water quality in karst regions using remote sensing and machine learning. The results show that surface water quality improved markedly, with the proportion of water bodies classified as the highest quality increasing from 22.7% to 35.9%. Attribution analysis indicates that pollution-related factors account for the dominant contribution across basins (> 65%), whereas climate effects are secondary and land-use contributions are generally small (< 5%). The number of people benefiting from high-quality water rose to 4.86 million by 2020, although 1.36 million people remained exposed to polluted water near expanding settlements. Future scenario projections indicate that these improvements may be reversed without sustained pollution control. These findings highlight the importance of protecting surface water in karst regions for ecosystem and human well-being. Surface water quality in China’s karst regions improved substantially, with top-quality waters increasing by up to 36 percent and 4.86 million people benefiting, but gains may reverse without continued controls, according to remote sensing and machine learning.