Huangshui Watershed Runoff Simulation Based On Swat Model

The runoff change under the Land use/land cover and climate change is animportant aspect of the hydrological process. The hydrological model as an effectivemeans of the runoff change research, through the construction of rainfall-runoffprocess, quantitatively evaluates the runoff change of the basin under the landuse/land change and climate change.The Huangshui River basin is located in the transition zone of the Tibet Plateauand the Loess plateau, and it is the largest first-tributary in the upper reaches of theYellow River. Influenced by the Global Warming, the national project of theReturning Farmland to Forests and Pastures, and implementation of WesternDevelopment Strategy by central government, the basin’s hydrologic process hasseen a obvious change because of significant the Land use/land cover change ofHuangshui Rvier basin since2000. In addition, the urban life-water, theconfiguration of the industry and agriculture has changed. So it is significant andnecessary to simulate and study the recent hydrological process by using thehydrologic model and it is a primary prerequisite for the basin water resourcemanagement and planning. Then it provides data support for government decisionand marking relevant policies and regulations.The aims of this thesis are to model the recent year’s hydrologic process of thebasin by the distributed hydrological model SWAT and to observe the changes of thebasin hydrological process upon the changes of the land use. And meanwhile, aftersetting the future scenarios of the land use and climate changes, analyzing thepotential change of the basin hydrologic process, several innovative achievementsare as follow:1. Through the sort through, analysis and statistics of the basin soil propertiesdata, the basin’s SWAT soil attribute database has been set up. And by using thestatistics and calculation of the basin climate data from1961to2010, the SWATclimate database has been established. At the same time, dealing with the soil data,the land use data and the DEM data of the basin helps to create the relational SWATspatial database of the basin.2. According to the segmental simulate of the hydrologic process from1986to2007, during the monthly simulation from1986to2000, the calibration averageefficiency coefficient NS(Nash-Sutcliffe) is0.84, and the validation average efficiency coefficient NS is0.77. During2001to2007’s monthly simulation, thecalibration average efficiency coefficient NS is0.8, and the validation averageefficiency coefficient NS is0.74. It turns out that the result is more than0.5, which isthe monthly application requirement of SWAT model. So the SWAT model can beused for the simulation study of the hydrologic process. The yearly result precision isbader than the monthly result precision, during the yearly simulation from1986to2000, the calibration average efficiency coefficient NS(Nash-Sutcliffe) is0.69, andthe validation average efficiency coefficient NS is0.65. During2001to2007’smonthly simulation, the calibration average efficiency coefficient NS is0.76, and thevalidation average efficiency coefficient NS is0.78, which is the yearly applicationrequirement of SWAT model.3. The paper has studied the basin’s runoff volume change by fixing one factorand changing the other with the intention of observing the change of the basin’srunoff volume under the circumstance that the land cover has been changing. Finally,it can be discovered that, the annual runoff volume increased0.03mm when the landuse has changed from1987to2000, and the annual runoff volume increased0.71mmfrom2000to2007.It can be found that both of the pair of the statistics are not thatobvious. The basin runoff decreased20.26mm, occupying19.30%of the referenceperiod runoff volume when the basin land use and climate both have changed. Thephenomenon has illustrated that the basin water resource volume has been decliningfor the past few years. Based on the study upon different ages, the runoff volumedidn’t change much between the late1980s and the1990s under the circumstancethat the land cover has changed. The increased0.23mm in1990s occupied about0.19%of the1980s’s. To compare with1980s’s, the early21st century’s runoffvolume decreased34.03mm, which is considerable and occupied about27.52%of1980s’s. The decrease of the basin’s runoff volume may be influenced by manyfactors, such as the increase of the evaporation along with the increase of thetemperature.4. Through the simulation of the nine land utilization structure scenes, it canbe found that the influence of the land use change to the runoff volume is very smalland mainly concentrate on June to October. Among the nine future land utilizationscenes, the one which increased most is scene eight; whose runoff volume is87.23mm and the increased volume is about2.24mm. The one which decreased mostis the scene two, the runoff volume is84.12mm and the decreased volume is about 0.87mm. Finally, the two scene’s occupations of the reference runoff volumerespectively are2.64%and1.02%.5. In the basin future climate scene study, which based on the past50yearsclimate tendency, it can be found that in the scene nine future climate when thetemperature increased0.72degree, the runoff volume decreased2.56mm, occupying3.01%of the reference runoff volume. When the temperature keeps unchanged, theprecipitation increased20%, the runoff volume increased22.84mm, when theprecipitation decreased20%, and the runoff volume decreased20.3mm. The volumechanges respectively occupied26.87%and23.88%of the reference runoff volume.Although the changes between the temperature and the precipitation cannot besimply compared, there is no doubt that the basin’s runoff volume is mainlycontrolled by the precipitation. Through the24future climate scenes which based onthe IPCC report, it can be concluded that. When the temperature increased but theprecipitation decreased or the temperature decreased along with the precipitation’sincrease, both of the two phenomena will have a synergistic effect upon aggravatingthe runoff volume change of the basin. On the contrary, when the temperatureincreased along with precipitation’s increase or the temperature decreased along withthe precipitation’s decrease, both of the two combination scenes will haveantagonistic effects upon weakening the runoff volume change of the basin.