北京山区侧柏林冠层对降雨动力学特征的影响

林冠层枝叶对雨滴的能量要进行再次分配，从而在降雨雨滴大小分布、降落速度及动能等性质上都发生了变化，是森林水文生态功能的重要环节。然而目前国内外在森林影响降雨动力学特征方面的研究较少且研究方法不够完善。研究地点设在北京妙峰山林场，利用激光雨滴谱仪对侧柏人工林林内和林外进行了长期同步观测，对典型场降雨中林内与林外雨滴的数量、大小、速度、动能等动力学特征值进行了对比分析。结果表明：林内的雨滴总数高于林外37.8%，林内小径级和大径级的雨滴数目都有所增加，而中间径级雨滴减少。林外降雨体积贡献率随雨滴直径增加呈单峰曲线变化，而林内降雨呈多峰山状变化；在试验侧柏林下雨滴的终点速度有所减小，特别是对直径0.75-4.5mm范围的雨滴更为明显。林内降雨相比于林外其雨滴直径与雨滴终点速度的相关性降低，雨滴谱分布更加分散；林外降雨动能贡献值随雨滴直径增加呈单峰曲线变化趋势，而林内降雨呈多峰山状变化。在雨滴终点速度为4-9m/s的区间内林外雨滴贡献的动能明显高于林内降雨。侧柏林地雨滴降落到地面的动能比林外空旷地减少了27.0%，林内雨滴动能减小的最主要原因是林冠层削减了林内降雨量。

Research on changes of dynamic characteristics of rainfall though Platycladus Orientalis plantation canopy in Beijing Mountain Area

Due to forest canopy layer redistributes the energy of rainfall, the size distribution, terminal velocity and kinetic energy of raindrops change through the canopy. These changes are important part of the ecological hydrology functions of forest. However, at home and abroad, there is less studies on forest affecting the dynamic characteristic of rainfall is less, and the research methods are always imperfect. This study, performed at the Miaofeng Mountain forest farm in Beijing, used two laser raindrop spectrometers to synchronously monitor precipitation both inside and outside a Platycladus orientalis plantation, and analyzed the size, amount, velocity, kinetic energy and other dynamic characteristics of raindrops outside and inside forest for the typical rainfall events. The results show the amount of raindrops outside forest was 37.8% above inside forest, the amount of small and big diameter raindrops increased inside forest, but the middle diameter raindrops decreased. The rainfall volume contribution outside forest showed unimodal curve with the increase of raindrop diameter change, but that showed polymodal curve inside forest. The terminal velocity reduced inside forest, especially for the raindrops with diameter in the range of 0.75-4.5 mm. Compared with outside forest, the correlation between the diameter and terminal velocity of raindrops inside forest was reduced, and the raindrop spectrum distribution was more scattered. The rainfall kinetic energy contribution outside forest showed unimodal curve with the increase of raindrop diameter change, but that showed polymodal curve inside forest. When the raindrops terminal velocity was in the range of 4-9m/s, the kinetic energy contribution of the raindrops outside forest was obviously higher than inside forest. The total kinetic energy of the raindrop fallen on the ground inside the Platycladus orientalis plantation was 27.0% less than outside forest, and the main reason of that is the forest canopy cut down the precipitation inside forest.