| As the ninth national centeral city,Xi'an plays an important role in the development of the northwestern region.Also,this city accerate the urban agglomeration of the Guanzhong Plain.The rapid urbanization and expansion of the urban scale have led to significant changes in the pattern of land use,which has changed the conditions of the underlying surface and caused profound changes.Rainfall,infiltration,runoff and other water cycle processes directly affecting urban water systems and river morphology.Changes of these factors may cause a series of urban hydrology and water resources problems,it is necessary to research the impact of urbanization on the underlying surface,river system and hydrological characteristics of Xi'an.Based on the collected materials we use ArcGIS,ERDAS,ENVI software dividing remote sensing images of different years(1995,2008,2016)into urban construction land,farmland,waters,gardens,forest land,and unused land.Based on the SCS hydrologic model,the land use change in different periods was established,and calculated the runoff of different land use types in different periods.And focus on the study of Ba river and Feng river basin which is the greatest influence of urbanization.By ArcGIS and TauDEM analyzed the water patterns and river network characteristics in the 1960 s,1990s,and 2010 s,studied the effects of Xi'an urbanization on the rainfall,runoff in the Feng-Ba River basin.The main conclusions of this research are shown as follows:From analysis of collected data,Xi'an's urbanization has shown rapid growth in many aspects such as population,economy,and proportion of cities and towns from the founding of the People's Republic of China.Using ERDAS and ArcGIS and ENVI software for interpretation,found that during the period of 1995 ~ 2016,Xi 'an urban construction land,garden land area increases,the cultivated land and unused land and water area decreased,most of the cultivated land and unused land into urban construction land,which has caused drastic changes in the underlying surface of the city,and the infiltration capacity and the impregnability of the city's underlying surface have changed accordingly.Based on the SCS-CN model,simulated the runoff changes caused by land use changes at different times in Xi'an,and found that the total runoff showed an increasing trend,and found that the increase of urban construction land and farmland,forest land reduction played an important roles which resulted in increased the total runoff.Comparing the river network conditions in different periods of 1960 s,1990s,and 2010 s,it was found that the density of river network,water surface rate,river average length ratio,and branch ratio decreased.The statistical analysis shows that the river network structure has the following characteristics: The development of the river system has a certain self-similarity,the number of channels and the water level of the river network,and the average length of the river has an exponential relationship with the river network level;The overall structure of the water system tends to be simplified,and the number and length of the river level can be seen to increase the number and length of the main river;The higher the degree of urbanization area,the more obvious the reduction of drainage density,length,area ratio and the river network complexity.Field investigation found that the overall length of the upper reaches of the Feng-Ba river has been reduced,and rivers in some sections have been widened,and the shape of the river network has changed greatly.From the annual rainfall increase,precipitation coefficient and the rainfall rate difference in the suburbs,it was found that the rainfall rate during the flood season was significantly lower than the annual rainfall rate,shows that the impact of urbanization on the rainfall during the flood season was greater than the annual rainfall;The urbanization also increases the probability of strong precipitation in urban areas,and the mutation analysis of M-K and sliding T-test in the annual rainfall day,and the mutation in 1990 and 2009.According to the data of the monthly runoff volume of the elderly in the typical hydrological station of Feng and Ba river from 1956 to 2015,the research and analysis showed that the urbanization caused the increase of winter runoff and the decrease of spring runoff.The trend of Cu,CR,and Cv curves shows that the characteristics of urbanized Xi'an river runoff concentration have become significantly weaker.From the mutation analysis of Feng-ba river,the mutation points occurred in the late 1970 s,especially in the mid and late 1990 s which is the abrupt period of urbanization development.To sum up,there are various indications that the hydrological effects of the Xi'an River are closely related to the urbanization of Xi'an. |
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