The Numerical Simulation Of TheLulun Lake Watershed Hydrology In Inner Mongolia Under The Future Climate

Hulun lake which located in the Hulunbeir grassland in the eastern China, together with rivers constitute a variety of landscape including grassland,wetland and sand. Because of its location in plateau of cold and arid region, the shape, area and water quality of the lake suffer from negative influence due to the climate changes. In recent years, frequent human activity and surrounding environment changes have also effected Hulun lake negatively. As the most noticed phenomena the decline of water level and the shrinkage of area are observed. At present, the research of lake concentrated on the issue of pollution and eutrophication of lake in humid-subhumid region in the south of China, while insufficient attention are put on the widespread shrinkage and disappear problem of lake in arid and semi-arid region. The disappearing rate of lake of Inner Mongolia ranked second in the country after Xinjiang. Therefore, only a full understanding of the difference between north and south lake in hydrological processes and variation characteristics can help the government to take effective protection measures.In this paper, some researchs were undertaken on the current state of Hulun lake and its possible status in future climate, which include the following parts;First of all, in order to reduce the error in subsequent calculations, some basic processes were done on the data of the surrounding meteorological, hydrological site,for example, the method to calculate rainfall, evaporation of lake, verification of lake level-area-capacity relationship. On this basis, the research has differentiated lake hydrological processes according to climate seasonal variations and when necessary, merged and separated them with the intention of simplifying the water balance relationship, and at last gotten the hydrological features. Based on this, the projected water level of missing years is in good agreement with existing research results, which show that this is an effective way to obtain water level based on other informations. According to the results of analysis of climate change in the period from1960to2010, three climatic characteristics and the corresponding water balance items were built. After analyzing impact on water level under fully and single water balance items change between different climate characteristics, the reason of evident water level decline turned out to be the sharp reduction of river runoff.Secondly, with the prepared data required for HydroGeoSphere, multi-year average water balance items were used to build steady-state model. The simulated groundwater head, water network, surface water depth is in agreement with practical situation, which show that the steady-state model can capture hydrologic characteristics of the surface-subsurface water system of the study area and can be used as-initial conditions for transient flow. Based on2009data, the transient flow was used to calibrate parameter by adjusting hydraulic conductivity of hydrogeological unit and evapotranspiration parameters, at the same time the thaw and snowmelt process approach is also taken into account. The2010data was used to demonstrate the utility of HydroGeoSphere model to simulate the three-dimensional hydrologic response of the surface and subsurface flow systems, and then the comparative analysis of the seasonal variations of surface and subsurface exchange flux was discussed.Finally, the research has also compared the predicted short-term cliamte result of mean generating function and regional climate model, which show that the predicted resulte of mean generating function is consistent with actual situation. The data in the period from1961to2010were used for modeling, mean generating function was used to predict the rainfall and evaporation from2011to2030. The result show that there will be scarce rainfall and strong evaporation in2027,2029year, the watershed will dry; on the contrary, abundant rainfall, low evaporation in2022,2024, the basin is relatively moist. Daily rainfall in2024,2027were extracted from the PRECIS data, which are more than predicted results of the mean generating function. Penman formula used to calculate the evaporation based on other meteorological indicators from PRECIS data. The research has chosen average daily rainfall, evaporation of predicted result from mean generating function and daily various rainfall, evaporation from PRECIS data in2024,2027as boundary conditions in HydroGeoSphere model simulation, and then compared and analyzed seasonal variations of the suface water depth,saturation and runoff of Wuerxun river. In the next20years, there will be no extreme weather and the highest water level will reach543.2m in wet years, which will not cause the disaster, but improve the lake water environment, while the lowest lake water level will be539.4m in dry year, watershed soil will become dry.The application of water balance and surface-subsurface coupling model can help to obtain the seasonal variation of hydrological processes and distribution characteristics, which can be used as the basis for finding out the causes of lake shrinkage, while realization of possible status in future climate is important for the protection of water resources in cold and arid regions.