Evaporation meter - Evaporation meter

This is an instrument for measuring the amount of evaporation, and most of them measure the amount of water lost in a container. When the purpose of the observation is to measure evaporation from the natural ground surface, the container is set outdoors. A type A or large evaporation meter is commonly used, and is a metal basin with a diameter of 120 cm and a depth of about 25 cm. It is painted white, placed on a wooden frame, and placed outdoors. The water level is read every day with the attached gauge, and the difference from the previous day is calculated as the amount of evaporation. When it rains, the amount of rain is subtracted. Because heat flows in and out of the sides and bottom of the container, the amount of evaporation is greater than that of a natural water surface. Small evaporation meters with a diameter of 20 cm were also used in the past, but they show a greater amount of evaporation than large ones. There are also evaporation meters that use filter paper or porous ceramics with the surface moistened with water. A lysimeter is used to measure evapotranspiration from the ground on which plants and other things are present. In this case, the top of a container filled with soil is set to coincide with the ground surface, and the weight is measured.

[Takeji Shinohara]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

水の蒸発量を知るための計器で、容器に入れた水の減少を量る方式が多い。自然の地表面からの蒸発を知ることが観測の目的である場合には、容器を戸外にセットする。よく用いられるのは、直径が120センチメートルで深さが25センチメートルほどの金属製のたらいで、A型あるいは大型蒸発計とよばれる。白く塗り、木枠にのせて野外に置く。付属のゲージで毎日、水面の位置を読み取って前日差を求め、蒸発量とする。雨が降ったときはその量を差し引く。容器の側面や底面から熱の流出入があるため、自然の水面よりも過大な蒸発量になる。以前には直径が20センチメートルの小型蒸発計も用いられたが、大型よりも大きい蒸発量を示す。濾紙(ろし)や多孔質陶器の面を水で潤した蒸発計もある。植物などがある地面からの蒸発散を量るにはライシメーターが用いられる。これは、土を入れた容器の上面が地表面に一致するようにセットし、重量を測定するものである。

［篠原武次］

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