Abstract:

By using last 8 years daily rainfall data of Shanghai and an improved SCS model, the daily surface runoff of farmland was simulated, then the characteristics of runoff was analyzed. The main conclusions are as follows.The nonirrigated farmland in the antecedent moisture conditions of dry, almost saturated, saturated to produce surface runoff need rainfall 8.47, 3.58, 1.41 mm respectively.The soil moisture of paddy field are saturated,and the critical rainfall to resulting in runoff is 0.26 mm.The runoff distributions of nonirrigated farmland and paddy field are extremely right skewed.The maximum runoffs in nonirrigated farmland and paddy field are 135.59 and 1857 mm respectively.But the 9811% days of flow in nonirrigated farmland are less than 10 mm, the 9540% days of flow in paddy field are less than 20 mm.Annual flow is a bimodal distribution with the peaks in June and August, and there is a trend that the peak moves from August to June.Compared with the paddy field,the flow of nonirrigated farmland are more concentrated in May~September.There are about 50 days producing flow in nonirrigated farmland every year and the number is about 120 in paddy field. In general, the number of days producing flow continuously is not more than 5 in nonirrigated farmland,and not more than 7 days in paddy field.〖HJ1〗〖HJ〗