Spatial and temporal characteristics of non-point source pollution and risks in the drinking water source area: A case study of Heihe River in Xi'an

Climate change and human activities have posed challenges to the availability and quality of drinking water resources. In water-stressed regions of northern China, pollution in water source areas has significantly impacted public health and hindered socio-economic development. This study focuses on an important water source area in Xi'an city and utilizes high-resolution multi-source integrated remote sensing images from Google Earth and Sentinel-2 remote sensing data to interpret land use information in the water source area. The Analytic Hierarchy Process (AHP) and Non-Point Source Pollution Risks Index (NPPRI) method were employed to assess non-point source pollution risks and analyze their spatial distribution characteristics. Additionally, water quality data from 2011 to 2021 in the water source area were combined to analyze the impact of land use changes on water quality. The results indicate that most water quality indicators meet Class II standards, with total nitrogen being the main pollutant exceeding the standards, primarily originating from non-point sources such as domestic sewage, livestock, and agricultural fields within the region. The overall non-point source risk within the water source area is relatively low. The NPPRI is influenced by three factors: the proportion of non-point source risk areas within the first-level protection zone, the second-level protection zone, and the small watershed. High-risk level small watersheds are the main areas affected by non-point source pollution and should be given priority in management efforts. Therefore, based on the spatial distribution of risk factors, regional pollution prevention and control measures should be implemented to mitigate water source risks and ensure drinking water security. The research findings can provide data support for the refined management of water source area risks.