Green Water Response To Landuse And Climate Changes

Water resource in ecological hydrology usually divided into two categories:blue water and green water. blue water t is stored in the rivers and lakes,green water is from precipitation and returne to the atmosphere through evapotranspiration,often called "invisible water". Research for green water the is crucial for water security and food security in arid and semi-arid areas and has important significance for solving the water shortage and of problem.Presently, water resources assessment generally focus on the estimate of the blue water, that is liquid water in the traditional sense, while ignoring the gaseous water, that is green water assessment. Considering the green water in water resources Assessment, which is conducive to a more comprehensive assessment for water resources, and might help for solve the water scarcity.In this study, the upper reaches of the Du watershed was selected as the study area. Combined with GIS spatial analysis, hydrological modeling was conducted in study area using SWAT (Soil and Water Assessment Tool) model. Analyse the evolution of green water. Estimating the green water resources at different scale in Du watershed and analyse the response of green water distribution to land use and future climate change by using the SWAT. The conclusions are as follows:(1) The applicability analysis of SWAT model in Du watershed.Simulation in Du watershed was conducted using SWAT model by collecting and pre-processing the basic data and database preparation. Through DEM terrain analysis, extracting drainage and watershed discretization to determined the optimal division level. Set the sub-basin threshold value to4000ha, Set the hydrological response unit threshold value to2%of the land use,2%of the soil. Eventually, the Du Watershed was divided into107subbasins, which in turn were subdivided into674HRUs. Then loaded the land use, soil and climate data and completed the trial run of the model.In order to improve the applicability and accuracy of the model, parameter sensitivity analysis was conducted to get a more targeted parameter calibration. The results showed that ten parameters such as ALPHA_BF, CN2, ESCO have a significant effect on stream and five parameters such as CH_COV, CH_EROD have a significant effect on sediment.Based on the results of the parameter sensitivity analysis, calibrate parameters that have significant impact. The6-year time period from1965to1970was selected perform warm-up of the model. Streamflow and sediment calibration and validation were performed for the periods1971-1980and1981-1990, respectively. Compared the calibration and validation results with evaluation criteria, the efficiency coefficient ENS of streamflow in the calibration is0.88, the relative error Re is0.02, the determination coefficient R2is0.94, the validation period of streamflow efficiency coefficient are0.87,0.1,0.92, respectively. The efficiency coefficient ENS of sediment in the calibration period is0.67, the relative error Re is0.29, the determination coefficient R2is0.84, validation period are0.64,0.37,0.81, respectively. The ENS, Re and R2values showed adequate results for both the calibration and the validation. periods. The model has applicability in the Du watershed.(2) Green water distribution under the landuse change.Analysis the four periods land-use change rule in the study area from the area, the rate and the structure. The results showed that forest has largest variation from1978to2007. Forest, grassland and shrubland decreased before1999and the area devoted to farmland increased. However, after1999the forest, grassland and shrubland began to increase while the amount of farmland decreased due to the Grain to Green Program, which was the largest land retirement program implemented in China.The change of green water flow and green water resources in the study area have been simulated under different land use scenarios. The results showed that green water flow and green water resources tended to increase with the increase of forest area and reduction of farmland. Green water flow increased from371mm to469.6mm during1978to2007period, green water increased from376mm to474mm.Forest evapotranspiration is greater than farmland. Forest evapotranspiration is the biggest, while the streamflow would decrease accordingly. Therefore, ecological restoration should focus on afforestation in Du watershed.(3) Green water distribution under the Climate changeBased on the general trend of global climate change and combined with the forecast of future climate change in China to build different climate scenarios to simulate and study area. The results showed that:with the increase of the temperature and rainfall, green water flow and green water resources keep increasing. The impact of precipitation variation on the rate of change is bigger than temperature. At the same temperature, the impact of precipitation on green water is more apparent.(4) Temporal and spatial distribution of green water resources.The subbasin was selected as simulation scale. Analyze the cheractristics of green water temporal and spatial distribution. It showed that the green water resources in Du watershed account for50.5percent of the total precipitation. The green water flow account for87.6percent of green water resources. It is indicated that most of the water resources dissipation is evapotranspiration, including invalid evapotranspiration that is difficult to use. The green water distribution trend is similar to the rainfall. Green water account for53.1percent of total green water resources and green water storage is evenly distributed. Green water flow and green water resources in south of study area are that in the north. Green water storage of northern is bigger than that in the south of Du watershed.