By taking Caijiachuan watershed on the Loess Plateau of Western Shanxi Province

as the study object

the relationship between rainfall and runoff and the water balance in the experimental watershed were studied using statistical methods such as multiple comparison and regression analysis for the data of precipitation and runoff measured in the watershed from 2004 to 2009.Results showed that the percentage of yearly water consumption was 90% more than yearly rainfall.Water consumption appeared to be the main water output in the water cycle of the experimental watershed.The yearly runoff coefficient ranged only from 1.6% to 2.66%.Runoff and peak discharge for a single rainfall event changed evidently with changes in the magnitude order of rainfall amount(P) and the maximum 60-min rainfall intensity(I60) in a jump mode.Specifically

runoff volume and peak discharge for P≥30 mm rainfall were about 8.31 and 6.52 times of those for the 0~10 mm order of rainfall amount

respectively.Runoff volume and peak discharge for I60≥20 mm/h rainfall intensity were about 3.35 and 16.87 times of those for the 0~10 mm/h order of rainfall intensity

respectively.Regression analysis of runoff

peak discharge

and rainfall indexes under different types of rainfall showed that the contribution of rainfall intensity to peak discharge was highest(47.12%) under A-type rainfall(stom events with short duration and high intensity) as compared to that under B-type rainfall(storm events with long duration and high intensity

44.62%) and C-type rainfall(storm events with long duration and low intensity

32.51%)

while the contribution of rainfall amount to runoff was highest(28.5%) under C-type rainfall as compared to that under A-type rainfall(26.69%) and B-type rainfall(3.15%).