Objective With the intensification of global climate change and human activities, water pollution has become one of the most critical environmental challenges worldwide. As one of China's most economically developed and densely populated regions, the Beijing−Tianjin−Hebei area faces increasingly severe issues such as water scarcity, deteriorating water quality, and degraded aquatic ecosystems due to rapid urbanization and industrialization. This study aims to guide the rational allocation and efficient utilization of water resources, providing scientific basis for regional water environment management and ecological conservation.

Methods This study employs total phosphorus (TP) output as an indicator of water purification capacity. Utilizing the Integrated Valuation of Ecosystem and Trade−offs (InVEST) model, spatial autocorrelation analysis, and the Spatio−temporal Geographically Weighted Regression (GTWR) model, it examines the spatiotemporal evolution of water purification capacity and the spatiotemporal heterogeneity of influencing factors within the Beijing−Tianjin−Hebei region.

Results Phosphorus output in the northwestern mountainous areas was lower than in the southeastern plains, with high−value zones primarily distributed in the foothill plains. Phosphorus output showed little temporal variation between 1990 and 2020, while phosphorus output per unit area exhibited a decreasing trend, indicating enhanced water purification capacity in the Beijing−Tianjin−Hebei region. Phosphorus output demonstrated significant “high−high” and “low−low” clustering characteristics. Spatio−temporal geographically weighted regression (GTWR) analysis revealed that factors with significant positive effects on phosphorus output were, in order: elevation, precipitation, index of dispersion and juxtaposition (IJI), and patch density (PD). Factors with significant negative effects were, in order: number of patches (NP), population density, mean area ratio of patches (PARA_MN), and patch richness density (PRD).

Conclusions Based on the spatiotemporal heterogeneity of influencing factors, recommendations for enhancing water purification capacity are proposed across vegetation conservation and restoration, land−use planning and landscape pattern optimization, water resource management, and population and industrial regulation. These findings aim to provide reference for high−quality development in the Beijing−Tianjin−Hebei region.