Evaluation of land‐use change effects on runoff and soil erosion of a hilly basin — the Yanhe River in the Chinese Loess Plateau

Starting in 1999, the Grain‐for‐Green Programme has been implemented in the Loess Plateau to alleviate the severe soil erosion by converting steeply sloping croplands to forestlands or grasslands. To quantify the effects of these conservation efforts, this study identified the land‐use changes between 2000 and 2015 and quantified their impacts on runoff and erosion using the Soil and Water Assessment Tools (SWAT) and a typical hilly basin, the Yanhe River basin as a case‐study. To heighten the applicability of SWAT to the region, major model parameters were localized and calibrated for the period of 1975–1980 and were then validated for 1981–1987. The R2 and NS validation indices were 0.70 and 0.65 for the monthly runoff and 0.67 and 0.61 for the sediment load, indicating that the model performance was acceptable. Between 2000 and 2015, the slope croplands were reduced by 39.9%, the forestlands increased by 90.2%, and the grasslands increased by 12.9%. These land‐use changes were simulated using SWAT to reduce the basin runoff by 13.8% and the sediment load by 50.7%. Spatial analyses using ArcGIS indicated that the simulated reduction in water yield due to cropland conversion to forestland was more obvious than that due to the conversion to grassland, but the reductions in the sediment yields were similar. The results suggest that the Grain‐for‐Green practice during this period was effective for preventing soil and water losses.