Reference crop evapotranspiration (Etref) is a fundamental variable in the hydrological cycle. Accurate estimation of Etref is essential to water resources project planning and farm irrigation scheduling. Based on the daily meteorological data from 123 climatic stations across Northwest China in the period of 1971-2000 and the reference crop evapotranspiration calculated by Penman-Monteith equation served as a standard, the 20 cm pan coefficient Kp was estimated by relative humidity and wind speed. And Kp model was respectively built and verified at different levels of single station, sub-region, and the whole study region. Results showed that there was a strong linear correlation between pan evaporation and reference crop evapotranspiration in Northwest China, and the correlation coefficients were 0.967. Kp model for sub-region was more accuracy than that for the whole study region, and was more suitable than that for single station. Thus Kp model for sub-region was recommend for estimating Etref in large area.%参考作物蒸散是水文循环的重要参量,它的准确估算对于农业水资源的合理规划和利用尤为关键.本文利用西北干旱半干旱地区123个气象台站1971-2000年的逐日气象观测资料,以FAO推荐的Penman-Monteith公式确定的参考作物蒸散为标准,建立了基于相对湿度与10 m高度处风速的由20 cm小型蒸发皿换算参考作物蒸散的Kp模型.结果表明:西北地区参考作物蒸散ETref与蒸发皿蒸发Epan的相关系数达到0.967,两者之间存在明显的线性相关关系.与单站模型和全区模型相比,分区域Kp模型的精度介于两者之间,同时具有一定的推广价值,建议使用.
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