Water resources planning driven by eco-hydrology theorem: A case study of Ziya River basin

Traditional water resources planning usually focuses on “blue water” in the hydrologic cycle, ignoring “green water” which accounts for over 60% of the hydrologic cycle. The method of water resources planning at watershed scale based on the concept of eco-hydrology involves a comprehensive analysis of a combined system composed of water resources, social economy and ecological environment through water consumption management to attain sustainable regional development. This paper, from the precipitation of watershed, analyzed the conversion of precipitation from “blue water” to “green water” and constructed a watershed-scale water resources planning model based on the concept of eco-hydrology that contained water resources system module, social economy system module and ecological environment system module. The computation of “green water”, which is the core module of the water resources planning model, adopted the Penman-Monteith model based on the Leaf Area Index (LAI) of MODIS remote sensing and optimized parameters based on the spatial differences of vegetation in the watershed. The “green water” computation was achieved through the transformation of water from the traditional evapotranspiration model at a single-point scale to a multiple-point scale of the watershed evapotranspiration model. Also the processes spatial and temporal variations of two key parameters, including soil evapotranspiration coefficient and vegetation stomatal conductance, were established. Finally, the model was used to simulate water resources planning in a watershed, which involving the actual water consumption by vegetation ecology, residential use, industrial production, food production and different trees/grass. By using Ziya River basin as a case study and 2008 as the reference year, the paper calibrated and verified the parameters of the model and the relative error between the monthly simulated and measured evaporation of different vegetation types (7%), which proved that the model had an acceptable simulation accuracy. By matching planting structure, water-saving irrigation regime, industrial structure, residential water use and aquaculture water use with engineering measures of the middle line of the South-to-North Water Transfer Project, the constructed water resources planning model was used to quantify different planning measures. The results showed that under 50%–75% rate of assurance, water use by natural vegetation was 8.82–7.63 billion m³, that by agriculture was 14.21–12.68 billion m³ and those by urban life, industrial production, tertiary industry and rural life were respectively 0.79, 0.26, 0.31 and 0.33 billion m³. Water consumption in Ziya River basin dropped by 1.19 billion m³ under 75% assurance rate and by 1.32 billion m³ under 50% assurance rate after the implementation of the planning measures. Agricultural production (as the largest water consumer) contributed the most to the water consumption cut, which reached 0.76 billion m³ under 75% assurance rate and 0.88 billion m³ under 50% assurance rate after using the planning measures. This was at least 60% of the total water consumption cut, indicating that the adjustment of planting structure and irrigation pattern was critical in cutting down water consumption in Ziya River basin. The results of the study provided necessary technical support for the efficient and sustainable utilization of water resources in watershed.