中文摘要：

滦河流域下游冷口站以上流域下垫面条件发生了明显的变化，导致洪峰和洪量均有减小的趋势．根据冷口站以上流域水文气象及下垫面特征，结合流域的超渗-蓄满产流机制，建立了考虑下垫面条件的流域水文模型，并对模型进行了参数率定和模型验证，结果表明模型具有一定的精度．利用该模型分别模拟了1980年前后下垫面条件下的若干场次洪水，经过对比分析，下垫面变化导致洪峰平均减小16.9%，洪量平均减小9.9%，且洪峰和洪量减小程度随洪量的增加而减小，通过模拟1980年前后土地利用条件下的各场次洪水，分析了土地利用变化和水土保持工程分别对洪峰和洪量的影响程度，结果表明冷口站以上流域洪峰和洪量的减小主要是由水土保持工程引起的．

英文摘要：

The underlying surface has changed in the Lengkou catchment,a sub-catchment of Luanhe River basin, which has led to a decreasing trend in flood peak and volume. According to the hydro-meteorological characterization and infiltration excess-saturation excess runoff generation mechanism,a hydrological model was established in which underlying surface components were taken into account. The model was calibrated and verified by using historical hydrological data,and it is of enough precision to analyze the effect of underlying surface change on flood. Many large floods were selected and simulated under underlying surface conditions before and after 1980,respectively, and the results were compared. It is shown that flood peak and volume declined by 16.9% and 9.9%,respectively, and the decrease magnitudes of flood peak and volume reduce with the increase of flood volume. We also analyzed the effects of land use change and soil and water conservation projects on flood peak and volume by modeling the histori-cal floods under underlying surface conditions before and after 1980. It is indicated that in Lengkou catchment,soil and water conservation projects are the main reasons for flood decrease.