The flood response process under heavy rains is extremely complicated due to steep slopes and variable vegetation coverage in mountainous area and the runoff convergence time in the slope has become a key parameter in flood process simulation. The most widely used flow concentration time formula at present isT=L0.6n0.6i-0.4S-0.3, whereTis the flow concentration time,Lis the slope length,nis the roughness, i is the effective rainfall intensity andSis the slope. The current studies generallyly use a constant index of rainfall intensity to characterize runoff convergence time while few study considers the slope and vegetation abundance effects. In this work we conducted a series of indoor experiments to study overland flow concentration under different slopes and vegetation coverage conditions. In addition, the variation rules of runoff convergence time parameters are analyzed as well. The results show that the fitting value of rain intensity index represented for the impact of rain intensity on confluence time is about-0.40 on the 45° and 30° slope, which is consistent with frequently-used results of previous research. However, when it comes to the 15° and 5° slopes, the fitting values of rain intensity index turn into-0.30 and-0.25 respectively, which is slightly larger than that used in the common approaches. The further investigation under conditions with vegetation suggests that rain intensity index changes obviously with the existence of vegetation: while on slopes of 45°, 30ånd 15°, the average fitting value of rain intensity index falls to-0.63 when vegetation coverage is 50% or above, significantly less than the theoretical value of-0.4; the mean value of rain intensity index in 20% coverage is about-0.37, almost the same as that in vegetation-free situation. In addition, rain intensity index under 5° slope condition for different vegetation coverage is relatively stable at values between-0.30 and-0.25.
