九龙山侧柏林林内降雨时滞效应

Time lag effect of rainfall inside Platycladus orientalis forest of Jiulong Mountain

在北京九龙山试验场地布设HOBO RG3-M自计式翻斗雨量筒,利用2012年7月21日至2013年10月1日期间侧柏林林内外实时降雨过程的定点观测数据,研究典型场降雨和特大暴雨极端天气下的侧柏林内降雨的时滞效应特征.结果表明,在具有完整降雨数据的56场降雨中,降雨初始阶段,林内降雨均晚于林外降雨,降雨量级为小雨时,林外降雨发生延迟约51.42 min后才产生林内降雨,而降雨量级为大雨以上时,林内降雨产生延迟仅约19.40 min,两者相差近3倍.随着降雨量级的增大,降雨开始阶段,林内降雨延迟时间逐渐缩短;降雨结束阶段,林内降雨延迟时间逐渐增加.通过对林内降雨延滞开始时间和延滞期雨强进行拟合,得出两者之间存在较好的对数函数递减关系;但对降雨延滞结束时间和场降雨量二者进行相关分析,并未发现二者存在明显的相关性.在典型场降雨中,不同降雨强度(暴雨、大雨、中雨、小雨)下,林冠层对侧柏林内降雨的雨强峰值出现时间起到了一定的延滞作用.特大暴雨极端天气下,降雨强度最强时林内雨强较林外雨强小,可见林冠层对强降雨雨滴的动能起到了一定的缓冲作用.由于林冠层对大气降雨存在延滞作用,能有效地延迟地表径流和土壤水文入渗的产生,对减少土壤侵蚀、防止水土流失、减少山洪、泥石流和滑坡等地质灾害具有一定的实际意义.

To investigate time lag effect of forest on rainfall especially potential application in mitigating extreme rainstorm,HOBO RG3-M data logging rain gauge was set up at test site in Beijing Jiulong Mountain,and real-time rainfall data,including rainfall in-tensity and start and end time of rain inside and outside Platycladus orient alis forest were recorded from July 2 1 ,2012 to October 1, 2013. A total of 56 rainfalls with complete data were obtained. When precipitation was low,rainfall inside the forest occurred 51.42 min later than the outside,while it was only delayed for 19.40 min when precipitation was high,which was shortened to L/3 of the former. With increased rainfall intensity,delay time was shortened gradually at the beginning of rain and increased gradually at the end of rain. A logarithmic function relationship between delay time at the start of the rain and rainfall intensity was found but no cor-relation between delay time at the end of the rain and rainfall intensity. In different intensities of rainfalls （torrential, heav^^, moder-ate ,light rain）,canopy delayed the peak of rain inside P.orientalis forest to some extent. Especially in extreme rainstorm,internal rainfall intensity inside forest was lower than the outside when rainfall was most intense. Thus canopy plays a certain buffer effect on the kinetic energy of heavy rainfall. To summarize,canopy delays surface runoff and soil hydrological infiltration and it has some practical significance in preventing soil erosion,and reducing mountain torrents,debris flow and landslides.