Study on scale effect of flood runoff coefficient

Runoff coefficient is a very important parameter to describe runoff dynamics.The scale effects on runoff coefficients have been observed by several researchers on plots or small watershed,however,little research has been done on meso-scale and large-scale catchments.So six meso-scale and large-scale sub-basins of the Luanhe River Basin were selected for calculating the runoff coefficients of single event during 1956-2002.An obvious reduction in average event runoff coefficients from 0.43(Liuhe basin) to 0.10(Luanhe basin) was found with increasing basin area.Through the analysis,we show that the spatial variability of rainfall,the groundwater discharge ability and infiltration are the important factors leading to the decrease of runoff coefficients.The scale effects on runoff coefficient is very important to development of a physically-based hydrological model and flood control and disaster reduction.