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.