ET_0计算公式的设定条件和重要影响因子的实验率定研究

Experiment Research on the Presumed Conditions and the Important Factors of ET_0 Formulas

对ET0计算公式设定条件和重要影响因子的实验率定研究:揭示了Penman-Motheith(PM)等公式定义中叶面冠层阻力、反射率及Angstrom公式中的a、b值不是定值,而是一个随作物生长变值,并建议将变化的叶面冠层阻力、反射率及季节a、b值代入计算公式,可得到更加切合实际的ET0值;鉴于参考作物有两种:牧草和紫花苜蓿,不同的参考作物蒸发蒸腾量计算公式对应着不同的参考作物,求得两种参考作物蒸发蒸腾量的转换系数Kr可进行不同参考作物间的转换计算;揭露了参考作物(苜蓿)冠层光合有效辐射(PAR)及冠层顶部光合有效辐射(PARCAN)在一定程度上影响ET0值,气孔导度和物质积累等生理、生化作用也与ET0的变化过程十分相关;并对ET0标准ASCE-PM、PM、MP公式中主要气象输入因子对ET0、ETa、ETr值的潜在支配作用进行了研究。有助于ET0学科中重要问题的引领研究及精确估计。

This paper carries the experimental research on the calculation conditions and the major factors of ET0 formulas. It is revealed that the leaf surface resistance and the albedo in the Penman Montheith （PM） equation, and the value of a and b in the Angstrom equation are not constant, and they change with the crop growing stages. It is suggested to calculate the values of a and b, the surface resistance, and albedo according to the crop growing stages to obtain the actual ET0 . In view of the fact that there are two kinds of reference crops： grass and alfalfa, for the two evapotranspiration formulas, it is necessary to calculate the conversion coefficient Kr to transform between the two equations for different reference crops. The values of PAR and PARCAN of reference crop （alfalfa） to certain extent have influences on ET0 value; stomata conduction and material accumulation also change with ET0. The paper also conducts studies on the latent dominating effects of the major meteorological factors on ET0, ETa and ETr in the standard ASCE--PM, PM and MP formulas. These results are helpful for ET0 studies and estimates.