Climate change amplifies the impacts of anthropogenic inputs on nitrogen loading in global rivers

Riverine nitrogen (N) loading is increasing rapidly due to both climate change and human activities, posing severe threats to global water quality. However, the contributions of precipitation, temperature and their interactions in driving these increases remain insufficiently understood at global scale. Here, we establish a Global River Nitrogen and Discharge (GRIND) observations database and develop a machine learning model to generate high-resolution (5-arcminute) spatially explicit estimates of global riverine N loading, using 14 explanatory predictors to elucidate the complex interactions between climate change and anthropogenic N inputs. Our findings show that the top 20% of high-loading river basins contribute 61% of global riverine N loading, among which 89% of these basins locate in regions experiencing high precipitation or intensive anthropogenic N inputs. Notably, rising precipitation and temperature amplify N loading in high-input regions, with the most significant effects occurring when precipitation ranges from 500 to 1500 mm yr⁻¹, and temperature and soil nitrogen content exceed 6°C and 450 cg/kg, respectively. Under future climate change scenarios, global riverine N loading is projected to increase by 0.5-3.6 Tg yr⁻¹ by the late century, even if current “business-as-usual” N input levels persist. Precipitation-driven increases are most pronounced in tropical and temperate regions between 40°S and 40°N, where an estimated 16.7±19.6% rise in N loading is expected, escalating water quality risks in these densely populated areas. In contrast, temperature-driven increases dominate in the Arctic region North of 60°N, exceeding 10%. To address the growing complexity of global water quality deterioration, we propose the Climate-Sensitive Nitrogen Reduction (CLEAN) framework, which identifies high-risk regions for future N loading and recommends strategies to mitigate the combined risks posed by climate change and human activities.