黄土高原典型树种幼树冠层对降雨雨滴特性的影响

Influence of young growth canopy of several typical tree species on rainfall characteristics in the Loess Plateau

为探索林冠层对降雨雨滴特性的影响,利用人工模拟降雨和色斑法,测得了栽植于土槽中的黄土高原典型树种侧柏、油松、元宝枫的4年生幼树树冠下降雨雨谱,并与林外降雨特性进行对比分析。结果表明：①与直径几乎都集中于1~3 mm的林外雨滴相比,树冠下的雨滴直径分布几乎不受林外降雨强度的影响,细小雨滴个数占绝大多数,直径1 mm以下的雨滴约占全体的40%左右;直径3 mm以上的雨滴约占全体的3%左右,所测到的最大雨滴直径为6.4 mm。②与裸地降雨相比,林冠下降雨的雨滴体积累计曲线明显分为两段,即林冠使得冠下降雨的大雨滴和小雨滴数量增多,而中等大小的雨滴数量变少。③3个树种林冠下降雨的体积累计分布曲线与雨强没有明显的函数关系,把其雨滴样不分雨强加以统计,得出不同树种各自的雨滴体积累计分布曲线。用Best模型拟合,得油松a=3.444,n=1.966,R2=0.982;侧柏a=4.038,n=2.164,R2=0.979;元宝枫a=3.881,n=1.885,R2=0.961。

The objective of this study is to understand the influence of tree canopy on raindrop characteristics for typical tree species on the Loess Plateau, including Platycladus orientalis, Pinus tabulaeformis and Acer truncatum. Artificial rainfall simulation experiment in laboratory and the splash method were used. The results showed that： 1 ） compared with open field raindrops, whose size mostly ranging between 1 and 3 mm, the raindrop size under tree canopy was hardly influenced by rainfall intensity and small size raindrops dominated the size distribution. The raindrops with a diameter less than 1 mm accounted for about 40% of all. The raindrops bigger than 3 mm accounted for 3 % and the maximum diameter of raindrops was 6.4 mm. 2） Compared with raindrops at bare filed, the raindrop volume cumulative curve under tree canopy had two distinct parts, i.e. when raindrops hit the canopy, some big raindrops occurred and meanwhile, some raindrops broke into pieces and then resulted in many small raindrops. Whereas middle size raindrops were not common. 3） There was no obvious function relationship between rainfall intensity and raindrop size distribution under the canopy of three tree species. Using all the raindrop samples without considering the effects of rainfall intensity, we can derive the raindrop volume distribution curves for three tree species based on Best＇s model as the followings：for P. tabulaeformis, the parameter values were a = 3.444, n = 1.966, R2 = 0.982; for P. orientalis, a = 4.038, n = 2. 164, R2 = 0. 979 ;for A. truneatum, a = 3. 881, n = 1. 885, R2 = 0. 961.