Comparison of Actual Evapotranspiration Estimated by Inverse Analysis versus Penman Evaporation and Complementary Relationship Evapotranspiration

― Case study by Hokkaido, Tohoku, Kanto and Shikoku national agricultural research institute data ―

Abstract

This paper describes that a comparison between actual evapotranspiration (ETa) estimated by inverse analysis, recently proposed method by authors, versus the penman evaporation (Ep) and the complementary relationship evapotranspiration (Eac) using four sites climate data during about ten years. After confirming the reasonability of the daily ETa and Ep relationship, the monthly changes of the ETa/Ep estimated, resulting in the ratio is 0.7~0.9 during from April to October. And the monthly changes of the ratio exhibit almost the same through the sites. After confirming the relationship of daily and monthly change for ETa and Eac using energy load coefficient 1.26, the relationship presents that the yearly change of the Eac and ETa is almost coincided each other. Subsequently, we conducted the optimum determination of the coefficient by comparing the sum of daily ETa and Eac data, resulting in the coefficients 1.23~1.37. Then, the coefficients apply the four sites, resulting in the ETa and Eac very well coincided. From the above analysis we concluded that complementary relationship Eac is strongly supported by the inverse analysis ETa. On the contrary, the inverse analysis is supported by the complementary relationship, if apply Eac>0 constrain for complementary relationship.