川西亚高山三个森林群落的湿林冠蒸发速率

Wet Canopy Evaporation Rate of Three Stands in the Western Sichuan

基于 3个假说和林冠上方 2m处的气象变量 ,采用Penman Monteith组合模型估算了一个生长季节内川西亚高山林区分别以云杉 (SF)、冷杉 (FF)和白桦 (BF)为优势树种的 3个林分的湿林冠蒸发速率 (Er)。研究结果表明 ,SF、FF和BF的湿林冠蒸发量 (E)分别为 4 4 5mm、88 5mm和 5 7 8mm ,分别占总降雨量的 9 2 %、16 6 %和10 2 %。与SF和BF相比 ,FF具有最高的月平均Er和蒸发比例。SF、FF和BF的平均Er分别为 0 0 97mm/h(变化范围 :0 0 2 8～ 0 4 87mm/h)、0 2 4 2mm/h (变化范围 :0 0 6 8～ 0 711mm/h)和 0 14 9mm/h (0 0 6 0～ 0 5 76mm/h)。最高和最低的月平均Er分别在 6月 (SF、FF和BF分别为 0 12 0mm/h、0 317mm/h和 0 16 9mm/h)和10月 (SF、FF和BF分别为 0 0 83mm/h、0 187mm/h和 0 10 1mm/h)。 8:0 0至 16 :0 0期间的平均Er显著高于0 :0 0至 8:0 0以及 16 :0 0至 0 :0 0期间的平均Er。Er显著的日变化和月变化主要归因于林冠上方的太阳辐射。

Rainfall interception by canopy is governed by two important parts: one is the specific water interception capacity on the surface of foliage, twig, branches and trunk; and the other is the wet canopy evaporation rate during rainfall events. Numerous studies during the past decades have led to the general conclusion that wet canopy evaporation(E) contributes greatly to rainfall interception. E is a continuous and dynamic course controlled directly by a combination of meteorological variables and canopy structure. It implies that more attention should be paid to the wet canopy evaporation rate(Er) for each rainfall event in studying crown interception. However, E has been omitted in many studies, it is difficult to understand the rainfall interception in the canopy. Therefore, based on three assumptions, the Er of three stands, dominat ed by spruce (SF), fir (FF) and birch (BF) trees, respectively, were calculated by Penman-Monteith combination model based on meteorological variables 2 m above the canopy within a growing season. Results showed that: (1) the total amount of the E was 44.5 mm, 88.5 mm and 57.8 mm and accounted for 9.2%, 16.6% and 10.2% of the gross rainfall for SF, FF and BF, respectively, during the measuring period; (2) there was the highest average monthly Er and percentage of E to gross rainfall for FF, compared with SF and BF; (3) mean Er was 0.097 mm/h (ranged from 0.028 to 0.487 mm/h), 0.242 mm/h (from 0.068 to 0.711 mm/h) and 0.149 mm/h (0.060 to 0.576 mm/h) for SF, FF and BF, respectively; (4) the highest and lowest average monthly Er occurred in June (0.120 mm/h for SF, 0.317 mm/h for FF and 0.169 mm/h for BF ) and in October (0.083 mm/h for SF, 0.187 mm/h for FF and 0.101 mm/h for BF), respectively; and (5) the averages of Er from 8:00 to 16:00 were significantly higher than that from 0:00 to 8:00 and from 16:00 to 0:00 for three stands. The marked daily and monthly differences of Er were contributable to the variations of solar radiation, air temperature and relative humidity.