Abstract: Recent years, the expansion of impermeable surface area and the construction waterscape engineering caused by urbanization have made a great influence on regional hydrometeorology, water resource redistribution and river hydrological process. Therefore, evaluating the effects of urbanization has important implications for the sustainable utilization of water resources. Most of the researches on the effects of urbanization were oriented toward qualitative analysis which still remained fragmented. Based on the precipitation data of Xi'an City from 1970 to 2015, runoff data of Bahe River from 1970 to 2015, and land use data from 1995 to 2014, this paper analyzed the changing characteristics of precipitation, runoff, and land use of Xi'an by using linear regression, Mann-Kendall test, trend analysis, the cumulative departure method, land-use transfer matrix and land-use degree comprehensive index. Then the hydrological characteristic parameter-time series method was used to study the changes of relationship between precipitation and runoff. The results show as follows:(1)from 1970 to 2015, the change of precipitation in Bahe River did not present an obvious decreasing trend, but the change of runoff presented an obvious decreasing trend; (2)the land use intensity in Xi'an was strong and the land use type tended to conversion from farmland and forest land to construction land; (3)affected by urbanization, the precipitation mechanism in Xi'an changed, both the frequency of extreme heavy precipitation event and the yearly uneven degree of precipitation distribution presented a trend of increase, especially in the urban area, which may carry serious urban waterlogging risk; (4)urbanization has an effect on the relationship between precipitation and runoff in Bahe River, the influence of precipitation on runoff showed a weakening trend, while the effect of land use change on rainfall presented an increasing trend; during the urbanization effecting period, the fluctuation of runoff within a year became moderated, especially in the flood seasons; (5)in comparison to precipitation, urbanization played an dominant role on runoff, the effect of urbanization on runoff was 61.5%, while the effect of precipitation on runoff was 38.5%; construction of hydraulic engineering facilities and groundwater over-exploitation near the river were the main reasons for runoff decrease in Bahe River. In general, this paper evaluated the effects of urbanization on regional precipitation and river hydrological process in Xi'an by considering the integrity of hydrologic cycle, the results may provide references for the healthy development of Xi'an, as well as for exploring the law of the hydrologic cycle that is caused by urban construction.

Key words: urbanization, precipitation, hydrological process, runoff, Xi'an City, Bahe River