Proposal of Simple Measurement Method for Evaporation Rate by Using Oxygen Isotopic Ratio

Abstract

The purpose of this study is to develop simple method for estimating evaporation rates of water using oxygen isotopic ratio. From the laboratory test, strong negative correlation between average humidity and oxygen isotopic ratio change per unit evaporation rate was observed and humidity was clarified to be important parameter. The evaporation rate can be calculated from the amount of change of the oxygen isotopic ratio during evaporation. The amount of change of the oxygen isotopic ratio per unit the amount of change of evaporation rate estimated empirically under each humidity condition. The amount of evaporation per year in the Inawashiro Lake
in Fukushima was estimated to be 590mm/year from the relation between humidity and evaporation rate and the estimated value was in agreement with the calculation result of previous research, 600mm/year. Therefore, the simple estimation method is effective for estimation of evaporation rate of an actual lake or a pond especially in a dried area because the measurement error is small under the low humid condition.