Effects of climate and land use changes on runoff, sediment, nitrogen and phosphorus losses in the Haihe River Basin

Investigating the impacts of climate and land use changes on the hydrological cycle and water environment at the basin scale is important for providing scientific evidence to manage the trade-offs and synergies among water resources, agricultural production and environmental protection. We used the Soil and Water Assessment Tool (SWAT) with various spatiotemporal data to quantify the contributions of climate and land use changes to runoff, sediment, nitrogen (N) and phosphorus (P) losses in the Haihe River Basin since the 1980s. The results showed that 1) climate and land use changes significantly increased evapotranspiration (ET), transport loss, sediment input and output, and organic N and P production, with ET, sediment input and organic N affected the most; 2) runoff, sediment and ammonia N were most affected by climate and land use changes in the Daqing River Basin (217.3 mm), Nanyun River Basin (3917.3 tons) and Chaobai River Basin (87.6 kg/ha), respectively; 3) the impacts of climate and land use changes showed explicit spatiotemporal patterns. In the Daqing, Yongding and Nanyun River Basins, the contribution of climate change to runoff and sediment kept increasing, reaching 88.6%–98.2% and 63%–77.2%, respectively. In the Ziya and Chaobai River Basins, the contribution of land use was larger, reaching 88.6%–92.8% and 59.8%–92.7%, respectively. In the Yongding, Chaobai, Ziya and Daqing River Basins, the contribution of land use to N and P losses showed an increasing trend over the past 40 years (maximum 89.7%). By contrast, in Nanyun and Luanhe River Basins, the contribution of climate change to N and P losses increased more (maximum 92.1%). Our evaluation of the impacts of climate and land use changes on runoff, sediment, and N and P losses will help to support the optimization of land and water resources in the Haihe River Basin.