城市化对西安市降水及河流水文过程的影响

为探究城市化对西安市降水机制及城市河流灞河下游水文过程的影响，根据西安市及灞河1970-2015年水文气象资料以及由遥感影像解译得到的土地利用数据，在分析西安市降水、土地利用特征及灞河下游降水、径流变化特征的基础上，运用水文特征参数时间序列法分析城市化对西安市降水的影响以及灞河水文过程的影响。结果表明：1970-2015灞河降水量呈不显著下降趋势，而径流量呈显著下降趋势；西安市土地利用程度较高，土地利用变化表现为耕地及林地向建设用地转移；受城市化影响，西安市降水机制发生了改变，强降水频次呈增加趋势，且城区增幅大于郊区；降水年内分配不均匀，越来越集中于夏季，增加了城市内涝的威胁；城市化对灞河下游降水-径流关系产生了影响，降水对径流的影响呈减弱趋势，而城市化对径流的影响呈增强趋势；此外，受城市化影响，灞河下游径流量年内波动趋缓，特别是汛期；城市化是影响径流变化的主要因素（61.5%），降水变化是影响径流变化的次要因素（38.5%）；灞河下游径流量的减流主要是水利工程的作用及过量开采傍河地下水。

Effects of urbanization on regional precipitation and river hydrological process in Xi'an City

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.