Effects of climate change, crop planting structure, and agricultural management on runoff, sediment, nitrogen and phosphorus losses in the Hai-River Basin since the 1980s

Investigating the spatiotemporal changes in the eco-hydrological processes and environment, as well as their drivers, is essential to manage the trade-offs among water supply, agricultural production, and environment at a basin scale. In this study, we developed a framework based on the Soil and Water Assessment Tool (SWAT), together with the historical data, to evaluate the effects of changes in climate, crop planting structure, and agricultural managements on the eco-hydrological processes and environment in the Hai-River basin during 1985–2015. The results showed that an increase in temperature not only reduced runoff and sediment but also increased nitrogen and phosphorous losses in the river basin. By contrast, an increase in precipitation increased runoff directly and increased sediment and nitrogen and phosphorous losses indirectly. Runoff caused directly the difference between sediment and losses of nitrogen and phosphorous. Changes in crop planting area and fertilizer application rate affected positively the losses of nitrogen and phosphorous. Changes in irrigation area affected negatively runoff. Different crop species had different impacts on runoff and sediment. Increase in crop planting areas of maize and vegetable generally reduced runoff and sediment, while increase in crop planting areas of wheat and beans generally increased both runoff and sediment. The findings gain insights into the impacts and driving mechanisms of the changes in climate, land use, crop planting structure and agricultural management on runoff, sediment, and losses of nitrogen and phosphorus in the Hai-River basin.