Study On Rainfall Redistribution In Typical Forest Stands Of Nanjing Suburbs

This study set typical forests oak,Chinese fir,Pinus massoniana and bamboo as the researchobject.Throughfall,stemflow and canopy interception of different forest types were studied andanalyzed in the level of canopy layer.Explore the rainfall distribution process of canopy layer,aregression analysis was employed to select the main factors affecting rainfall distribution;studied the release effects of typical forests on rainfall erosivity in research area;greycorrelation was adopted to research the meteorological factors that affects the interception;Combined Gash model to simulate process of the rainfall interception,aimed to reveal themechanism that the structure of the forests influenced the rainfall input process.The conclusionas follows：(1) Fitting analysis method was used to research the relationship between precipitation andthroughfall(throughfall rate),stemflow(stemflow rate)and canopy interception(canopy intercept-tion rate).Precipitation had remarkable positive correlation with throughfall and stemflow,correlation is greater than0.9(P<0.01).The correlation of precipitation and interception isbetween0.628and0.860.Interception was significantly linear correlated with precipitation,Thecorrelation is between0.576and0.627and between0.584and0.618,respectively.The fittedregression equations showed that the minimum rainfall of4kind of forest necessary forthroughfall was1.20mm,1.13mm,1.21mm and1.85mm.Also analyse the relationship between rainfall and rainfall intensity.The correspondingrelationship between each level rainfall (rainfall intensity) and throughfall(throughfall rate),stemflow(stemflow rate)and canopy interception(canopy interception rate) were discussed.(2) Annual rainfall erosivity of the bare land was7912.68MJ mm hm-2h-1in the studyarea,in contrast to other research area it was small relatively.The rainfall erosivity in the oak,Chinese fir,Pinus massoniana and bamboo forest were78.71%,65.30%,73.99%and66.54%ofthe bare land,respectively.Forest land showed more significant result than the bare land inreducing soil and water erosion.4kinds of forest diminished21.29%,34.70%,26.01%and33.46%of the annual rainfall erosivity,respectively.Chinese fir and bamboo showed bettereffect in reducing soil and water erosion. (3) Based on grey correlation method to analyze the meteorological factors that influencedcanopy interception,the influencing priority of meteorological factors for4kinds of forest isknown.The experimental results revealed that precipitation,rainfall intensity,wind speed andrelative humidity had remarkable influence on canopy interception of4kinds of forest and netradiation showed less influence on canopy interception.The relationships between canopyinterception and meteorological factors appeared very complicated.Correlation analysis results show that, there was a significant negative correlation betweenthe canopy interception of oak,Chinese fir,Pinus massoniana and bamboo and precipitation，rainfall intensity and rainfall duration.We can conclude from stepwise regression equation,the most critical influence factor forcanopy interception rate of4kinds of forest is rainfall intensity and rainfall duration in thestudy area.The monthly mean canopy interception of4kinds of forest was not significantcompared with LAI,showed certain trends only.Monthly mean canopy interception ratedecreased with the increase of monthly mean LAI.(4) To improve the efficiency of the method,the Gash model had be applied.The canopyevaporation rate of forest were different in different fores,and the amount of canopy evaporationrate was between0.11mm/h and0.23mm/h.Compared with the measured values and theestimated values,the estimated value of4kinds of forest were13.22%,28.07%,21.29%and21.62%,less than the measured values1.13%,2.09%,1.19%and1.40%, respectly.The goodagreement between the estimated and measured values indicated that Gash’s analytical model issuitable for estimating interception losses.Sensitivity analysis indicated that the biggest impactof the parameters on canopy interception was canopy storage coefficient.