The Study Of The Yellow River Valley Runoff In Ningxia Hui Autonomous Region Based On SWAT Model

The Yellow River valley in Ningxia is a national important grain base. The Yellow river, which flows into Inner Mongolia after through Shizuishan town enters into Ningxia Hui Autonomous region in Zhongwei town. The valley covers cities of Yinchuan, Zhongwei, Shizuishan, Wuzhong, and Yuanzhou of Guyuan. With flat terrain, free canals, and the alluvial plain, its altitude is1100-2500m above sea level. It is variable arid zone that the annual average sunshine hours is between2750-2950h and annual average wind speed is between1.7-2.5m·s-1. There are sufficient sunshine and quantity of heat. Temperature difference is big, and the frost-free period is long. With an average annual precipitation of180-220mm, the river basin is continental climate, drought and the annual precipitation gradually reduces from north to south. It is relatively significant and uneven distribution of monthly precipitation difference of the Yellow River irrigation area. While the drought zone in central and southern mountains change relatively moderate and often happens seasonal rainfall changes. The precipitation from July through September accounts for60-70%of annual precipitation which leads to obvious dry season and wet season, and also to strong evaporation that can reach to1100-1600mm average annual. However, the water shortage is becoming more serious due to the growing population, increasing industrial and agricultural water use. and water pollution in recent decades. Because the water resource is related with the runoff of the Yellow River, therefore, it is an urgent need to study the changes of runoff of the Yellow River in Ningxia and fully understand the intrinsic factors affecting basin runoff, to realize the sustainably utilization of water resources. SWAT model is a physically based, semi-distributed parameter and watershed-scale model that works on continuous daily time step. It can simulate hydrological processes, sediment yield, nutrient loss, and pesticide loss into surface and groundwater, and the effects of agricultural management practices on water in large watersheds. SWAT incorporates the effects of weather, surface runoff, crop growth, transpiration, irrigation, groundwater flow, nutrient loading, pesticide loading, water routing as well as the long-term effects of varying agricultural management practices. In order to use the water resource more efficiently, the SWAT model was built to make the water change more clearly. Then Nash-Sutcliffe efficiency coefficient (Ens) and linear correlation coefficient (R2) were used to evaluate the applicability of the model in this valley. When the model has been built, keeping other database unchanged, the area of paddy field, irrigated land, dry land, forest land, shrub and grass changes respectively as the following8kinds of scenarios:1) increasing5%,2) increasing10%,3) increasing15%,4) increasing20%,5) decreasing5%,6) decreasing10%,7) decreasing15%,8) decreasing20%. Then, keeping other database unchanged, change the precipitation and temperature as that the precipitation increase by8%,16%,24%and32%and decrease by8%,16%,24%,32%, meanwhile, the air temperature increase by0.5℃,1℃,1.5℃and2℃and decrease by0.5℃,1℃,1.5℃and2℃. After each scenarios imposed, the change of runoff was recorded. And the main conclusions are as follows:1) The main parameters of the SWAT model based on the valley condition of the Yellow River in Ningxia Hui Autonomous were obtained, including Moisture condition Ⅱ curve number, Available water capacity, and so on.2) The SWAT model can be applied in the Yellow River valley in Ningxia Hui Autonomous. All of the R2and Ens each year meet the requirement of the SWAT model to use.3) The increased grass and shrub land area can increase the runoff. The grass makes the runoff change more apparently than shrub land. And the grass land is first choice to extend in paddy field, irrigated land, dry land, forest land, shrub land and grass land in the research area.4) Increased precipitation and decreased temperature can increase the runoff. And decreased precipitation and increased temperature can decrease the runoff.Through analyzing the results of the study and combining with the actual situation of the study area, three aspects of advice were put forward which contain the cultivation of grass and bushes that can grow in dry and alkali field, flood and drought warning, timely adjusting the strategy in the utilization of water resource and the research about relationship between each type of land cover and runoff. In addition, SWAT model has more strong function which may resolve some unsolved problems in the Yellow River valley in Ningxia. Combining with the current research results, outlook for future research was done. It contains the study of the influence of soil texture on runoff, coupling with the WRAP model and WEAP model, the study about the relationship between the runoff and other land cover types.