A research team led by Professor Yongqiu Xia from the Institute of Soil Science, Chinese Academy of Sciences, used the team’s independently developed Zhiyuan agricultural non-point source pollution model (Water Network Framework, WNF) to examine how climate change may alter cropland nitrogen pollution across China. By integrating 1,485 field observations with spatially explicit models to examine how climate change may alter cropland nitrogen pollution across China. Their findings show that emerging pollution hotspots are likely to shift from the humid south toward arid and semi-arid northern regions.
Nitrogen that is not taken up by crops can accumulate in soils and be washed into rivers, lakes, and reservoirs during rainfall. Because southern China receives more rainfall and has denser drainage networks, it has long been regarded as the country’s main hotspot of cropland nitrogen pollution. Northern drylands, by contrast, have generally been considered less vulnerable because limited rainfall restricts runoff and nitrogen transport.
This historical pattern may not persist under climate change. Rising temperatures can accelerate soil nitrogen mineralization, while increasing rainfall and more intense storms can mobilize nitrogen that has accumulated during dry periods. At the same time, lakes, reservoirs, and rivers can remove part of the nitrogen during transport, meaning that future pollution depends on the balance between terrestrial runoff and aquatic removal.
To capture this balance, the team linked models of cropland nitrogen runoff with simulations of nitrogen transport and removal through aquatic networks. The results showed that the humid south currently exports about 0.31 Tg of cropland nitrogen to the ocean each year, nearly twice the 0.16 Tg exported from the arid north. By 2050, however, northern nitrogen export is projected to increase by 18.8% under SSP2-4.5 and by 53.2% under SSP5-8.5, while southern export remains stable or declines slightly. In the Hai River Basin, the increase could reach 88.1% under the high-emission scenario.
The researchers explained that regions with the highest pollution today may not experience the fastest growth in the future. In northern drylands, accumulated soil nitrogen can be rapidly flushed into rivers when rainfall activates previously disconnected runoff pathways.
The findings call for region-specific and climate-adaptive management. Northern regions should prioritize weather-responsive fertilization, controlled-release fertilizers, and split applications to reduce nitrogen buildup before heavy rainfall. Southern regions should combine source reduction with riparian wetland restoration, aquatic vegetation management, and decentralized retention systems to maintain nitrogen removal within dense water networks. Similar risks may also emerge in other dryland agricultural regions, including the North American Great Plains and Australia’s wheat belt, although their magnitude and management implications require region-specific assessment.
National Science Review
Computational simulation/modeling