Green/blue water allocation as affected by Grain-for-Green practices in the upper reaches of the Yiluo River

Land use/cover change (LUCC) is of significant impact on regional water cycle. Land use decision-making is water resources decision-making, which has been confirmed by many studies and recognized by researchers and decision makers. Taking the upper reaches of Yiluo River in the middle reaches of the Yellow River Basin as the case study area, this paper applied the distributed watershed agricultural eco-hydrological model SWAT (Soil and Water Assessment Tool). According to the important background of ecological restoration and reconstruction of Grain-for-Green in China, six different land use change scenarios were set up to study the impact of land use/cover change on watershed water cycle from the perspective of blue/green water. This paper calibrated and validated the monthly runoff output of SWAT model, and proved that the model achieved acceptable accuracy and rationality in simulating the hydrological cycle of the river basin. One-way ANOVA and multiple comparisons were used to analyze the effects of land use change on the changes of various hydrological factors based on different hydrological years. The results showed that:1) From 2010 to 2015, the annual average precipitation resources was 3.494 billion m³, and the annual average of total blue water and green water resources was 3.409 billion m³. Blue water resources accounted for 33.73%, and green water resources accounted for 66.27% of the total blue water and green water resources in multi-year average. 2) Under different scenarios of Grain-for-Green, the amount of blue water resources decreased, the green water flow increased, and the green reservoirs decreased. In the year of the wet year and normal year, the impact of land use/cover change on the surface runoff component of the blue water resources was more obvious. This conclusion has certain significance for deepening the understanding of the relationship between land use/cover and water resources in the upper reaches of the Yiluo River, and provides a scientific basis for efficient and rational utilization of water and soil resources in the region.