Spatiotemporal Distributions of Blue and Green Water Resources
蓝水绿水资源量估算方法及时空分布规律研究

Current studies regarding water resources primarily focus on the qualification of blue water, but seem to pay less attention to green water which should be taken as a part of water resources and particularly is of importance to rain-fed agriculture and ecological systems. Spatially and temporally detailed analysis of different components of water resources are essential for decision-making in water resources planning and management. Blue water is defined as visible liquid water moving above and below the ground in the form of surface or sub-surface runoff, respectively. Green water is referred to as invisible vapor moving to the atmosphere including green water flow and green water storage. In this study, both blue and green water were considered in water resources assessment, which would be helpful for addressing the problem of water shortage. Through an analysis on assessment methods for blue and green water resources, it was considered that the Soil Water Assessment Tool (SWAT), a semi-distributed hydrological model, was one of most promising and efficient tools to estimate blue and green water resources. The SWAT model was used to simulate hydrologic processes in the Lushi watershed, a semi-arid to semi-humid area located in the upstream of the Yiluo River basin. In the light of the definition of blue water and green water, blue water can be equal to the water yield of surface and ground water, green water flow can be taken as actual evapotranspiration (ET), and green water storage can be regarded as the soil water storage estimated by the SWAT model. The SWAT model was used to estimate blue and green water resources in the Lushi watershed. Both spatial and temporal distributions of blue and green water resources were analyzed in detail. Results showed that 1) the amount of blue and green water resources is generally 9 times of the amount of conventional water resources in the Lushi watershed; 2) the annual blue and green water in the Lushi watershed peaks in flood season, and is lowest in winter. The green water flow is a major part of green water resources; and 3) the green water storage capacity is relatively larger in well-vegetated areas than that over other areas. Moreover, the concept of blue and green water resources provides stakeholders with a new means for efficiently utilizing and allocating water resources. On the basis of the spatial and temporal distributions of blue and green water, optimum utilization of water resources may be achieved through improvement in water management by reducing inefficient green water and increasing available blue water resources.