Studys On Rainfall Redistribution Of Typical Forest Stands In The Southern Slope Of The Qinling Mountains

The study set Pinus tabulaeformis,Quercus aliena var.acuteserrata,Picea wilsonii Mast.and Betula albosinensis were selected as the subjects.From the forest canopy level,the penetration rainfall of different stand plots in Qin Mountains was measured,in the growing season（May-october）of throughfall and interception,the effects of canopy on rainfall redistribution in different forest types were studied,the single factor analysis method was used to analyze the factors affecting rainfall redistribution,and the mitigation effect of typical stand on secondary rainfall erosivity was studied,in order to reveal the mechanism of rainfall redistribution influenced by different forest types,a multi-factor analysis of the meteorological factors affecting interception was carried out,and the process of rainfall interception was simulated with Gash model.The specific conclusions are as follows:（1）The relationship between rainfall and penetration rainfall rate,throughfall rate and interception rate in four stands of P.tabulaeformis,Q.aliena var.acuteserrata,P.wilsonii Mast.and B.albosinensis was fitted,the linear relationship between rainfall and throughfall,throughfall was very significant,R² was more than 0.9（p<0.01）,and the Linear independence between rainfall and interception was also significant,R² was more than 0.8（p<0.01）There was also a significant correlation between rainfall and penetration rate,with R² ranging from 0.488 to 0.668（p<0.01）,the relationships between rainfall and rainfall intensity and penetration rainfall rate,throughfall rate and interception rate were analyzed.According to the linear regression equation,the minimum rainfall required for the formation of stemflow was calculated.The minimum rainfall for the formation of penetrating rain in P.tabulaeformis,Q.aliena var.acuteserrata,P.wilsonii Mast.and B.albosinensis forests was 1.23 mm,1.32 mm,1.04 mm and 1.85 mm respectively.（2）The annual rainfall erosivity of the forestless land in the study area of Huoditang and Pingheliang were 2601.14 MJ·mm·hm^-2·h^-1 and 2494.61 MJ·mm·hm^-2·h^-1,respectively.Compared with the average annual rainfall erosivity of 2000-4000 MJ·mm·hm^-2·h^-1 on the south slope of Qin Mountains,the rainfall erosivity of the study area was moderate.The rainfall erosivity of P.tabulaeformis,Q.aliena var.acuteserrata,P.wilsonii Mast.and B.albosinensis Forest were 80.02%,53.30%,86.06%and 59.78%of that of no-forest forest,respectively.The effect of soil and water loss mitigation of forest land was more significant than that of no-forest land.The rainfall erosivity of four forests decreased by 19.98%,46.70%,13.94%and 40.22%,respectively.（3）The effect of each factor on crown interception rate in P.tabulaeformis,Q.aliena var.acuteserrata,P.wilsonii Mast.and B.albosinensis forest is in order of rainfall>intensity>rainfall interval.Among the four forest types,the least significant factor was net radiation.There was a significant negative correlation between canopy interception rate,rainfall duration and intensity in sharp-toothed oak forest,oil pine forest,red birch forest and green brimstone forest.The intensity and duration of rainfall are the most common and critical factors affecting the retention of forest canopy.（4）The average canopy evaporation rate for the four forest types ranged from 0.08mm/h to 0.21 mm/h.The Gash model results compared to the measured canopy interception rates showed that the canopy interception rates of P.tabulaeformis,Q.aliena var.acuteserrata,P.wilsonii Mast.and B.albosinensis were 14.23%,25.36%,12.66%and28.07%,respectively,below the measured values of 1.23%,1.59%,1.23%and 1.20%,respectively.The results of sensitivity analysis showed that the water holding capacity of branches and leaves was the most important parameter to affect interception of P.wilsonii Mast.forest.The average evaporation rate（E）of saturated canopy was the most important parameter affecting interception of P.tabulaeformis,Q.aliena var.acuteserrata and B.albosinensis.