Forest-hydrological Study on Transpiration in a Mountainous Watershed

本文以一个森林流域为例，尝试用三种方法估算山地小流域的蒸腾速率，以详细描述森林的蒸腾作用。在吉柳试验流域，采用短期水量平衡法和截留降雨观测估算了年和月蒸腾速率。在这项研究中，蒸腾速率已估计使用Penman-Monteith模型与以上的日本赤松和日本柏树混交林林冠层观测的气象数据。在吉柳流域的气象观测塔周围进行了树干液流流速的热脉冲法测定，利用由手持计算机和继电器开关输出的A/D转换器组成的热脉冲流速自动测定系统，连续测定了2年多的树干液流流速。蒸腾速率的季节变化特征 ...更多信息 三种方法估算的TE值吻合较好。Penman-Monteith法和树干液流测定法测定的蒸腾日变化也一致。然而，Penman-Monteith法估算的树干液流速率与树干液流测量值之间的关系呈非线性曲线。为准确估算热脉冲法的蒸腾速率，对一株日本扁柏进行了热脉冲法和吸水速率测定的同步观测。用一种简单的方法计算出的吸水率与热脉冲速度的关系曲线与Periman-Monteith法和热脉冲法估算值的关系曲线基本一致。通过对流扩散方程的数值计算，结合实际的热脉冲传输条件，建立了一个模拟模型，可以再现这种关系。少

Attempt has been made to estimate transpiration rate from mountainous watershed using three methods in a forested watershed for detail description on forest transpiration. In the Kiryu Experimental watershed, annual and monthly transpiration rate had been estimated by the short term water budget method and intercepted rainfall observation. In this study, transpiration rate has been estimated using the Penman-Monteith model with the meteorological data observed above the forest canopy in a mixed stand of Japanese Red Pine and Japanese Cypress. Measurement of sap flow velocity using the heat-pulse method also has been carried out around the tower for meteorological observation in the Kiryu watershed.Sap flow velocity using the heat-pulse method has been measured continuously more than two years by an automatic heat-pulse velocity measuring system composed of a handheld computer and a A-D converter with relay switch output. The characteristic of the seasonal variations in transpiration ra … More te estimated by these three methods agreed well one another. Diurnal variations in transpiration estimated by the Penman-Monteith method and by the sap flow measurement also agreed well. However, the relationships between estimated rate by the Penman-Monteith method and sap flow measurement shows a non-linear curve. The reason of the non-linear relationships may caused by the non-linear relationships between the heat-pulse velocity calculated by a simple method and the actual sap flow velocity.For the accurate estimation of transpiration rate using the heat- pulse method, simultaneous observation of heat-pulse method and water absorption rate measurement for a cut tree of Japanese Cypress has been conducted. The relationships between water absorption rate and the heat- pulse velocity calculated by a simple method shows is the nearly same curve as the relationships between estimated value by the Periman-Monteith method and the heat-pulse method. This relationships can be reproduced a simulation model using numerical calculation of an advection-diffusion equation with actual heat-pulse transfer conditions. Less