| In recent years, under the background of the global climate change, droughts have taken place frequently in the grassland area in northern China. At the same time, because of the excessive exploitation of groundwater, overgrazing and the development of industrial and mineral industry, the problems of water shortages and grassland degradation have been increasingly serious. The social and economic development of the regional and residents’ production and living have a serious threat. Therefore, quantitatively studying the effect of ecosystem degradation on water resources, it has very important application value and guiding significance for the local water resources evaluation, management planning and regional ecological research.This paper takes Xilinhe river basin within the territory of xilingol league area of northeast Inner Mongolia as the research area, studies the influence of the climate change and land use change on watershed hydrological processes.The purposes of the paper include:(1). Studying the applicability of the distributed hydrological model SWAT in Xilinhe river basin, and improved the model;(2). Detecting and analyzing the trends and characteristics of the climate change, hydrological changes and human activities(including land use change) of Xilinhe river basin in recent50years;(3). Under the change scenario of the climate change and the grassland vegetation, studying the response of watershed hydrological processes.The contents of the research include:using the trend analysis method, examined nearly50years the tendency of the climate change, land use/cover change and hydrological elements change; according to the semi-arid climate characteristics of basin and the effect that the freezing process of the seasonal frozen soil on soil moisture transfer, the hydrological model SWAT snowmelt and groundwater module had been carried on the corresponding modification; modified the default database of the land use/cover in the SWAT model, added including three types of coverage of the grass; by using the improved model to simulate the monthly runoff of the basin, and based on the hydrologic observation data of1963-1972, calibrated and validated the model. On this basis, presumed the different scenario of the climate change and grassland degradation, quantitatively simulated the influence of climate change and vegetation change on watershed hydrologic cycle, and then analyzed the response of watershed hydrological processes to climate change and grassland vegetation change.The main conclusions were as follows: 1. The climate of Xilinhe basin presents obviously the trend of warming and drying. From1961-2010, a total of50years, the precipitation declined at a rate of8.115mm/10a, while the temperature rosed at a rate of0.424℃/10a. In the same period, the annual average runoff depth had a slow decline at a rate of0.394mm/10a. Meanwhile, the grassland of the basin showed a trend of deterioration. During1987-2000, the meadow area decreased by65.94%, the typical steppe area declined by13.81%, but the desert grassland area increased by56.12%.2. The results showed that the simulated effect of the existing SWAT model in Xilinhe river basin in semi-arid areas was poor(Nash coefficient was-0.36, the determination coefficient was0.17), and the applicability was not good. We consider the climate characteristics of arid and semi-arid area, the hydrological cycle characteristics and the runoff mechanism of the basin under the condition of seasonal frozen soil, in view of the defects that when the distributed hydrological model SWAT simulated the spring snowmelt runoff process, correspondingly improved the type of grass cover, snowmelt, groundwater modules respectively, and increased the part of the frozen soil water storage. After improvement, the simulated flow curve was mainly consistent with the measured runoff curve, the flood peak of spring and summer could be corresponding. The mean Nash coefficient, determination coefficient and relative error are of the calibration period (1963-1967) respectively were:0.668,0.740,0.146, and the validation period (1968-1972) were:0.676,0.778,0.106. It could be concluded that the improved SWAT model was suitable for the Xilinhe river basin and the basins with similar geographical climate condition.3. By using the improved SWAT model to analyze the influence of the climate change on the runoff of the basin. Results showed that when precipitation increased by15%, then runoff increased by49.16%. When precipitation decreased by15%, and then the runoff decreased by41.79%. Temperature increased1℃,2℃and then runoff decreased respectively20.63%,37.54%.4. When the grass coverage reduced, the surface runoff increased significantly and the monthly volatility of the surface runoff also increased, namely the degraded grassland had the effect that the water increased. The extent that the surface runoff increased mainly related to how much of the precipitation. In more rainfall months, such as the July to August, the surface runoff increased more apparently. The average increased rate of the monthly average surface runoff in July to August was0.91m3/s, and that of other month (March-June, September-October) was0.78m3/s. In different period such as snowmelt and rainfall period, the influence that the grassland vegetation coverage on the runoff was not the same. Compared with the baseline period, after the grass coverage reduced, the growth of the surface runoff in snowmelt period was generally less than that in rainfall period. This is mainly because that the grassland vegetation coverage in snowmelt period in Xilingol is relatively lowest, but is highest in rainfall period. So the influence that the vegetation coverage on the surface runoff in snowmelt period is generally less than that in rainfall period.5. Using the regional climate model (HadCM model, A2emissions scenario) to simulate the future rainfall and temperature of the basin (2010-2100), the simulated results showed that under the A2scenario, temperature was clearly warming trend. During the period of2010to2100, temperature showed a trend of rapid increase with the rate of0.563℃/10a; precipitation was increasing trend with the rate of23.131mm/10a. Taking advantage of this climate simulated results, combined with changes in vegetation, driving the improved SWAT model, runoff was simulated. The results showed that during2010-2100, under the A2scenario, runoff (the grass maintain the present status)increased with the rate of0.029m3s-1/10a. |
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