干旱区生态环境知识资源中心

The irrigation of oasis fannland in arid regions mainly depend on water introduced by canals, so evaporation loss from canals is important to water resource, because long canals have been constructed for farmland irrigation and a large deal of water is evaporated from canal surface. In this study, canals in Zhangye (the middle reaches of Heihe River), Gansu, China were taken as the main research object, using data from automatic meteorological station (AWS) and remote sensing image, the evaporation from canal surface was estimated using a model which was under the rule of energy balance and proposed by Y. Mihara, results showed that: (1)when it was sunny, evaporation rate in the daytime was larger than that in the nighttime, but it didn't change a lot between daytime and nighttime when it was cloudy. Relative humidity was the key factor to the evaporation rate. (2) When it was sunny, cumulative evaporation in the daytime was about twice as much as that in the nighttime, but almost the same in daylight and at night when it was cloudy, humidity also had the greatest impact on this phenomenon.