中文摘要：

人类活动对于流域水文要素时变过程的影响显著，确定人类活动影响下水文要素时序的显著转折点、选出相对“天然”的序列，对于开展水土保持效益评价研究具有重要意义。以延河流域为例，采用数理统计方法推估获取人类活动影响下汛期径流时序的显著转折点，以显著转折点前的数据建立预测模型，对比分析汛期径流量的实测值与预测值，其差值即为人类活动对汛期径流的影响程度。较之传统研究方法，本文以汛期水文数据取代年均数据，．以汛期降水径流综合系数代替年径流系数，从而减弱了黄土高原地区降水、径流变化幅度巨大的干扰影响。结果表明，从20世纪50年代末至80年代末，1970年为人类活动下延河流域径流时序的显著转折点，1970年以后人类活动对流域水文的影响更显著，1981年达到最大值，为72．04％。20世纪70、80年代人类活动对延河汛期径流量的影响一直处于负面减流状态。人为因素是延河径流量演变的主要驱动因子。

英文摘要：

Human activities have great influence on runoff temporal change. The detected distinct transition point and relevant selected ＂unaffected＂ hydrological series that have great significance to assessment of soil and water conservation benefits. Taking Yarthe as an example, the distinct transition point of flood season runoff time series by the impacts of human activities has been detected by way of mathematical statistics analysis. And meanwhile, based on the datum before distinct transition point, the forecast model is set up only with the data series before the distinct transition point. The difference between the value derived from the equation and the observed value is right the influence on flood season runoff induced by human activities. Different from traditional methods, using hydrological datum and the synthesis coefficient of precipitation and runoff of flood season instead of annual ones, which could rationally weaken the impact of characteristics on rainfall and runoff in Loess Plateau. The analysis shows that 1970 is the transition point of runoff time series by impacts of human activities from the end of 1950s to 1980s, and human activities have affected significantly on hydrology of Yanhe basin since 1970.And in the year of 1981, human influence on river runoff reached maximum, with its value being 72.04%. In the 1970s and 1980s, flood season runoff was confined to reduced state at all times. So human factors is the primary one for the evolvement of Yarthe runoff.