庐山日本柳杉林下穿透雨时空分布特征

林冠是降水到达地面前的第一个作用层,其对降水的再分配作用,导致穿透雨的数量和空间分布具有很大的变异性,这既阻碍了对其的精确评估,也常常被认为是水文模型中蒸发量化的不确定来源之一。在庐山自然保护区日本柳杉(Cryptomeria japonica)人工林内设置了面积30 m×30 m的样地,机械布置了37个截面面积为314.15 cm2穿透雨收集器,于2017年生长季(4—9月)共监测21次降雨事件下穿透雨量。分析林冠下穿透雨率及其时空分布特征和影响因素。日本柳杉林下穿透雨率变化范围为2%—222%,平均穿透雨率为80%,穿透雨率随着林外次降雨量的增加而逐渐增大,降雨量达到28 mm时穿透雨率趋于最大值,之后变化规律复杂未见稳定,二者之间最优拟合关系为二次多项式;与叶面积指数呈显著负相关,叶面积指数小于4.5时对穿透雨率的影响显著。不同叶面积指数下,穿透雨率达到最大时的林外降雨量不同。穿透雨率的空间变异系数的变化范围为15%—114%,随林外降雨量的增加而减小,并在林外次降雨量大于20 mm以后,逐渐趋于稳定,二者之间以对数函数关系式拟合。观测点位的时间变异系数随着叶面积指数的增加而增大。叶面积指数小于5,降雨量小于20 mm时,降雨量是影响穿透雨空间变异性的关键因素。

Characteristics of the temporal and spatial distribution of the throughfall in Cryptomeria japonica forest in mount Lu

Precipitation redistribution is one of the most important effect of canopy interception, which caused the large variations of the quantity and spatial distribution of throughfall rain. This hinders both the accurate assessment of interception and is often considered to be one of the uncertain sources of evaporation quantification in hydrological models. A total of 37 gauges (cross-sectional area of 314.15 cm²) were mechanically arranged within a 30 m×30 m sample plot of Cryptomeria japonica stands in Mount Lu national natural reserve. During the 2017 growing season (April-September), a total of 21 rainfall events were monitored for rainfall. The results showed that the range of throughfall percentage varied between 2% and 222%, and the mean value was 80%. When the rainfall reaches 28 mm, the penetration rain rate tends to the maximum, and then the change law is complicated and not stable. The best fitting relationship between rainfall and throughfall could be described with a quadratic polynomial. Penetrating rain rate was significantly negatively correlated with the leaf area index. When the leaf area index was less than 4.5, the impact on the penetration rain rate was significant. Under different leaf area indexes, the rainfall outside the forest is different when the penetration rain rate reaches the maximum. The spatial variation coefficient of the penetration rain rate varies from 15% to 114%, which decreases with the increase of the rainfall outside the forest, and gradually stabilizes after the secondary rainfall outside the forest is greater than 20 mm. Logarithmic function relationship fitting. The coefficient of time variation of the observation points increases with the increase of the leaf area index.