PROPOSAL OF SIMPLE MEASUREMENT METHOD FOR EVAPORATIO RATE BY USING OXYGEN ISOTOPIC RATIO IN THE INAWASHIRO LAKE

Abstract

Using oxygen isotopic ratio and humidity, a new simple method of measurement for an evaporation rate in a lake is proposed. The oxygen isotopic ratio of the Inawashiro Lake is thought to have increased from -10.3‰ to -9.3‰ estimating from river flow rates and lake and river oxygen isotopic ratios. As a result of some evaporation experiments, the relation between evaporation ratio, initial oxygen isotopic ratio and humid was analyzed and then the evaporation ratio in the Inawashiro Lake was estimated 5.6 % from the relation and oxygen isotopic ratios. The evaporation in the Inawashiro Lake is calculated about 560 mm per year from 5.6 % evaporation ratio, lake inflow and lake area and is in agreement with that estimated by Jacob equation.