Assessment of Effective Green Water Resources in the Yangtze River Basin Based on Dynamic Crop Coefficient

The traditional water resources assessment mostly focused on the blue water that can meet the consumption of social and economic systems, ignoring the green water that can be used by plants. This traditional approach cannot fully reflect the full connotation of water resources, resulting in the lack of hierarchy in the caliber of the water resources assessment and directly leading to a large error in the division of effective green water. In this work, we presented an effective green water resource assessment method based on dynamic crop coefficient. The dynamic crop coefficient was introduced to improve the accuracy of green water simulation in the Yangtze River Basin. We validated the simulations against observed runoff and then the dynamic calculation of vegetation coverage was carried out to realize the division of effective green water resources in the Yangtze River Basin based on dynamic coverage calculation. The results showed that: (a) the SWAT model is an ideal tool to simulate runoff; (b) green water was the main water resource in the Yangtze River Basin. From 1961 to 2015, the average amount of green water resources was 957.7 billion m3, vegetation transpiration accounted for the highest proportion (590.7 billion m3), accounting for 90.7% of the total green water resources in the whole basin; (c) according to the division method of effective green water resources and the distribution of green water resources in different land use types, the effective green water resources in the Yangtze River basin were calculated to be 846.4 billion m3, accounting for 88.4% of the total green water resources in the basin, and the ineffective green water resources were 122.41 billion m3; (d) the evaluation method proposed in this study improved the accuracy of effective green water resources assessment, broadened the caliber of water resources assessment, and can provide more effective guidance for more effective utilization and scientific management of water resources.