Study On Rainfall Interception Characteristic Of Vegetation In A Typical Small Watershed,Upper Reach Of Heihe River Basin

Heihe River Basin is the second largest inland river, ensuring the water resources for socio-economic development of the western region. The upper reaches of the Heihe River is the significant water conservation area in the Heihe River Basin. Studying the upper reaches of the Heihe River Eco-hydrological processes make an important contribution for scientific water management. Canopy interception of vegetation play an important role in eco-hydrological processes. It is the first step of precipitation redistribution and affects the generation of runoff, soil water reserves and evapotranspiration. In this study, we choose three typical vegetation (Qinghai spruce forest, Potentilla fruticosa shrub community, Caragana jubata shrub community, and subalpine meadow) in Tianlaochi small watershed, which located in the upper reaches of the Heihe River Basin, as the research objects. Firstly, we study the interception characteristics of these three vegetation with artificial experiments and field observations. Secondly, based on canopy parameters and rainfall parameters, we establish the theoretical-experience or experience models to modeling the rainfall interception of each vegetation. Finally, in order to analyze the entire watershed vegetation interception characteristics, the established models are used to simulate the spatial distribution of canopy interception in Tianlaochi watershed, combining with the spatial distribution of relevant canopy parameters. The main conclusions are as follows:1) In our study watershed, LAI values of Qinghai spruce is in the range of0.0395to8.295, with an average of3.92; Total biomass of the alpine shrub is1.8×103t. with biomass per acreage of4230.21kg/hm2, shrub growing better in the sunny slope than the shady side; The biomass of subalpine meadow is grazing (464.89g/m2)> the grazing-prohibition (211.23g/m2), and species composition differ from grazing and grazing-prohibition meadows, the dominant species of grazing-prohibition meadow has weaker water storage capacity.2) The field data indicate that the average interception rate of Qinghai spruce in30×30m test plots is37.19%.When canopy is unsaturated, the average interception rate of Qinghai spruce is83.5%, then it drop to57.7%when the canopy reaches saturation. The average interception rate of alpine shrub in6×6m test plots the is Caragana jubata community (40.20%)> Potentilla fruticosa community(28.98%). the interception processes of the alpine meadows were linear increasing at first, after the appearance of throughfall (when the rainfall reached a value of1.80mm for the grazing-prohibition and1.10mm for the grazing meadows) the interception presented an exponential increase. The canopy interceptions for the grazing prohibition and grazing meadows are1.95mm and1.29mm.Canopy storage capacity measured by storage simple absorbent method for the grazing prohibition and grazing meadows are0.92mm and0.65mm.3) The results of simulated spatial distribution of canopy interception show that: in the growing season of2012, the average interception amount of Qinghai spruce forest is143mm, with the average interception rate of44.56%. The total rainfall interception amount of Qinghai spruce forest is3.92×105m3, accounting for the entire9.94%of the total rainfall of the entire basin. The average interception amount of alpine shrub is180.3mm, with the average interception rate of49.11%. The total rainfall interception amount of alpine shrub is about5.90×105m3, accounting for14.98%of the total rainfall of the entire basin. The interception amount of grazing and grazing-prohibition subalpine meadow range between50.12～53.75mm and65.40～72.53mm respectively, and their interception rate range between11.04～16.90%and16.23～22.08%respectively. The total rainfall interception amount of subalpine meadow in the case of grazing and grazing-prohibition were2.35x104m3and3.11×104m3respectively, each accounted for0.60%and0.79%of the total rainfall of the entire basin.4) In the case of grazing and the grazing-prohibition, the average interception amount of major vegetation in Tianlaochi watershed is156.82mm and157.65mm respectively, with average interception rate of45.35%and45.60%respectively. The total rainfall interception amount of the grazing and grazing-prohibition case is about10.13×105m3and10.19×105m3respectively, accounting for25.73%and25.86%of the total rainfall of the entire basin respectively. The pure meadow distribution area is so small that it contribute little to the overall interception amount. On the contrary, the alpine shrub contribute greatly to the interception of the study area because of its high interception rate and wide distribution.