Modeling energy fluxes from sparse canopies and understorys.
Modeling energy fluxes from sparse canopies and understorys.
复制标题
对稀疏树冠和林下植物的能量通量进行建模。
DOI：
10.2134/agronj2000.925837x
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发表时间：
2000
期刊：
影响因子：
2.1
通讯作者：
K. Mcnaughton
中科院分区：
文献类型：
--
作者：
C. Daamen;K. Mcnaughton
1986年）。地面阻力可以认为是平行的所有冠层叶片的等效阻力。地面是一个组合的表面类型，为（Monteith，1981）。Penman-Monteith方程可以举例说明林上植被物种、林下植被物种和裸露土壤。通常两种或两种以上的表面类型吸收一个显着的被施加在更一般的情况下，上层部分的可用能量的土地表面作为一个整体。在不同稀疏度的林冠中，如果这些情况下的表面阻力，来自各组成表面的通量的相互作用可能是大叶的等效阻力，所有贡献对总的陆地表面能量平衡是重要的。我们比较了上层林和下层林的表层元素。陆地表面能量平衡的三个模型：一个Penman-Monteith湍流transmodel的更详细的描述;一个模型有两个不相互作用的组成表面（植物冠层内的斑块端口过程由模型提出）;和一个模型有相互作用的组成表面（ShutRaupach（1989）使用拉格朗日理论。McNaughton泰勒-华莱士模型）。使用了六个已发表研究的数据，货车登·赫克（1995）应用劳帕奇的方法来研究在稀疏冠层的情况下，哪些模型最好地代表特定的陆地表面，并表明考虑到组件表面和上层冠层结构的供水的模型。图1a中给出的具有阻力结构的部件之间的通量相互作用是一致的，只有当与Raupach的工作有很大的关系时，才发现表面是重要的。该模型允许表面电阻之间的两个超差（即，具有不同性质和不同表面值的表面的水可用性）。此外，发现所有三个模型都估计了表面处相同的蒸汽密度（即，上层和地表能量通量（在50 W m22内），当两者都是地表下层时）。图1a中的电阻网络的电阻为.300 s m21。（Shuttleworth和Wallace（1985），Choudhury使用的冠层空气空间和参考高度之间的空气动力学阻力）与（平均值和Monteith（1988）以及随后对部件表面附面层阻力的几项研究）的比值，在他们的论文中是有用的。图1a中的网络允许组件表面之间的交互水平的交互。的通量从林下和上层的冠层气流，并在这项研究中被称为“互动”模式。M陆地表面有植被冠层。斑块模型（图1b）的复杂性介于Penman-Monteith模型和交互模型之间，不能完全覆盖林下植被。它或其下的地表，即稀疏层分别应用Penman-Monteith方程。此类表面包括耕地（例如，两个不同的组成表面，假设没有果园，葡萄园和许多行作物）和表面之间的自然相互作用。在最近的文献植被。自然植被具有稀疏的上层植被，该模型已被用于估计许多半干旱环境中的平均土地面积（例如，Nichols，1992年;在大面积（0.10平方公里）上面临通量，这些通量Massman，1992年; Brenner和Incoll，1997年）尽管可以用作气候中的边界条件，但这些冠层确实发生在其他环境中（例如，模型在这种情况下，蒸发量是通过分压湿地计算的，Lafeland和Rouse，1990年）。任何土地率为大均匀斑块和面积aversurface稀疏overstory至少有两个signifiage是从每个斑块类型的热量和水蒸气的加权倾斜源的蒸发：冠层本身的分数覆盖的斑块类型。斑块和林下植被或土壤。这两个组成部分surmodel是完全合理的规模，其中边界面往往是非常不同的，在他们的控制水层是充分发展，在每个补丁和边缘效应和热通量;都需要考虑补丁之间是微不足道的，但作为一个整体计算从陆地表面通量的大小。此外，补丁减少这个模型可能是不太有效。Blyth和Harding（1995）对虎灌丛地表的通量相互作用的研究可能很重要。例如，感热从裸露的土壤和灌木丛中升起。他们的结论是，一个干燥的土壤下层可以增加蒸腾作用，从互动模型已经比上层树冠更现实，通过提高其温度。虎灌丛的斑块模型，斑块与灌木高度之比为10：1。所需的斑块模型是由Penman-Monteith方程提供的，该方程开发了极端和不切实际的电阻值来保存，以估计来自封闭冠层的通量。（Monteith，1965）。与Blyth和Harneous的“大叶”表面具有单一的蒸汽密度值（1995）的上述结果相反，斑块模型已成功地用于表面的密度亏损（Jarvis和McNaughton，在植被稀疏的陆地表面的尺度上）。对于这些土地表面，组件表面（上层新西兰园艺和食品研究所有限公司，和林下植被）被视为斑块类型，即使P.O. Box 23，Kerikeri 0470，新西兰. 9月15日收到1999. * 通讯作者，现地址：Sinclair Knight Merz，P.O.没有明显的上层斑块，unBox 2500，马尔文3144，墨尔本，澳大利亚（cdaamen@skm. destory。Norman等人（1995）表明，差异com.au）。交互式和斑块模型之间的差异不大，从陆地表面的总通量在Agron出版。J. 92：837-847（2000）。
1986). The surface resistance can be considered to be the equivalent resistance of all canopy leaves in parallel Land surfaces are an assemblage of component surface types, for (Monteith, 1981). The Penman-Monteith equation can instance overstory vegetation species, understory vegetation species, and bare soil. Often two or more surface types absorb a significant be applied in the more general case of an overstory fraction of the available energy to the land surface as a whole. In canopy of varying sparseness if the surface resistance of these cases the interaction of fluxes from the component surfaces may the big leaf is an equivalent resistance of all contributing be important to the total land surface energy balance. We compare surface elements from overstory and understory. three models of land surface energy balance: a Penman-Monteith A much more detailed description of turbulent transmodel; a model with two component surfaces that don’t interact (patch port processes within plant canopies was presented by model); and a model with interacting component surfaces (ShutRaupach (1989) using Lagrangian theory. McNaughton tleworth-Wallace model). Data from six published studies are used and Van den Hurk (1995) applied Raupach’s approach to investigate which models best represent a particular land surface in the case of a sparse canopy and showed that a model taking account of water supply to the component surfaces and overstory canopy architecture. Flux interaction between component with the resistance structure given in Fig. 1a is consistent surfaces was only found to be important when there was a large with Raupach’s work. This model allows for two surdifference between the surface resistances (i.e., water availability to faces with different properties and different values of the surfaces). Also, all three models were found to estimate the same vapor density at the surface (i.e., an overstory and an land surface energy fluxes (to within 50 W m22) when both surface understory). The resistance network in Fig. 1a has been resistances were .300 s m21. The ratio of (aerodynamic resistance used by Shuttleworth and Wallace (1985), Choudhury between the canopy air space and the reference height) to (mean and Monteith (1988) and several studies following on component surface boundary layer resistance) was useful for indicatfrom their papers. The network in Fig. 1 a allows interacing the level of interaction between component surfaces. tion of fluxes from the understory and overstory in the canopy air stream and is called the “interactive” model in this study. M land surfaces have a canopy of vegetation The patch model (Fig. 1b) is intermediate in complexwhich does not completely cover the understory ity to the Penman-Monteith and interactive models. It or the ground surface beneath, that is, a sparse applies the Penman-Monteith equation separately to overstory. Such surfaces include cultivated land (e.g., two different component surfaces, assuming there is no orchards, vineyards, and many row crops) and natural interaction between the surfaces. In recent literature vegetation. Natural vegetation has a sparse overstory this model has been used to estimate average land surin many semiarid environments (e.g., Nichols, 1992; face fluxes over large areas (.10 km2), and these fluxes Massman, 1992; Brenner and Incoll, 1997) although can then be used as a boundary condition in climate these canopies do occur in other environments (e.g., models. In this context evaporation is calculated sepasubarctic wetland, Lafleur and Rouse, 1990). Any land rately for large homogeneous patches and the area aversurface with a sparse overstory has at least two signifiage is the evaporation from each patch type weighted cant sources of heat and water vapor: the canopy itself by the fractional cover of the patch type. The patch and the understory or soil. These two component surmodel is fully justified at the scale where a boundary faces are often very different in their control of water layer is fully developed over each patch and edge effects and heat fluxes; both need to be accounted for when between patches are insignificant, but as the size of the calculating a flux from the land surface as a whole. Also, patches decreases this model may be less valid. Blyth interaction of fluxes from the two component surfaces and Harding (1995) studied a tiger bush land surface may be important. For example sensible heat rising from with patches of bare soil and bush. They concluded that a dry soil understory can increase transpiration from the interactive model was already more realistic than the overstory canopy by raising its temperature. the patch model for tiger bush with a ratio (patch A simple approach to estimating land surface fluxes width):(bush height) of 10:1. The patch model required is provided by the Penman-Monteith equation which extreme and unrealistic values of resistances to preserve was developed to estimate fluxes from a closed canopy the measured fluxes. of vegetation (Monteith, 1965). It assumes a homogeIn contradiction to the above result of Blyth and Harneous ‘big leaf’ surface with a single value of vapor ding (1995), the patch model has been successfully used density deficit at the surface (Jarvis and McNaughton, at the scale of the sparsely-vegetated land surface. For these land surfaces the component surfaces (overstory The Horticulture and Food Research Institute of New Zealand Ltd., and understory) are treated like patch types even though P.O. Box 23, Kerikeri 0470, New Zealand. Received 15 Sept. 1999. *Corresponding author, current address: Sinclair Knight Merz, P.O. there are no distinct patches of overstory and unBox 2500, Malvern 3144, Melbourne, Australia (cdaamen@skm. derstory. Norman et al. (1995) showed that differences com.au). between the interactive and patch models made little difference to total flux from the land surface at the Published in Agron. J. 92:837–847 (2000).