Analysis of Evapotranspiration Process for Working System Planning in Water Resources Conservation

本研究从根本上采用了三种方法对蒸散发进行分析。第一个是用涡动相关法分析实际数据直接测量蒸散量的研究，第二个是将短期水量平衡法应用于日降水量和日径流量的研究，最后一个是分析日径流量的流量持续时间曲线的研究。在爱知县大学森林和琵琶湖东侧木本镇两个研究地点，对起伏地形上的林冠湍流输运进行了测量。用涡流相关法测得的动量τ和感热H的湍流通量来检验体体法的拟合优度。结果表明，对于tau和u的u^*的相关关系，林场数据样地分布较广，且与稳定性密切相关，而平场数据满足线性相关。利用爱知大学森林两个小实验流域56年的流量记录，试图确定一长串流量持续时间曲线的趋势，以描述物理过程随森林生长逐渐变化的影响。采用简单回归模型进行对比分析，发现两个流域在流量历时曲线上第6 ~ 220天的流量在几十年间呈线性增加趋势。采用短期水量平衡法对日流量和降水资料进行蒸散计算。用简单模型对流域湿度差异进行校正后，发现3个流域林分蓄积量与蒸散指示值之间存在较好的关系。

In this study three methods were adopted to analyze evapotranspiration fundamentally. The first one is a study analyzing actual data with eddy correlation method to measure directly evapotranspiration, the second is a study to apply short term water balance method to daily precipitation and daily runoff, and the last is a study to analyze discharge duration curve on daily discharge rate.1.Measurement was conducted to turbulent transport on forest crown which locate on rolling terrain in two study sites, University Forest in Aichi and Kinomoto Town in east side of Biwa Lake. Turbulent flux of momentum tau and sensible heat H which was measured by eddy correlation method were used to check goodness of fit on bulk method. The result shows that as to the correlation between u^* from tau and U,the data plots of the forest site were scattered widely, and were closely related to stability, however, the flat field data satisfied the linear correlation.2.Attempt has been made to identify trends in a long series of discharge duration curve for describing the effect of gradual change in physical processes with forest growth using 56-year discharge records in two small experimental watersheds in the University Forest in Aichi. It was found that the 6th to 220th day discharge on the discharge duration curve linearly increased over the course of several decades in both watersheds using comparative analysis with simple regression models.3.Short term water balance method was applied to the data of daily discharge and precipitation to get evapotranspiration. After correcting the difference caused by watershed wetness with simple model, good relationship between stand stock of forest and indication value on evapotranspiration was found in three watersheds.