中文摘要：

运用Penman-Monteith方法,对北京昌平、开封惠北及湖北团林3个灌排试验站的近几十年参考作物腾发量（ET0）进行计算,结果显示,惠北及团林站年均ET0在近几十年呈现随时间而下降的趋势,而昌平站年均ET0则随时间而上升。ET0与同步气象资料变化分析表明,ET0的上述变化是由于气象环境变化所引起,其中相对湿度是最主要原因,其次为温度及日照时数。对昌平站,由于相对湿度的降低和风速的增加,ET0表现出上升的趋势;对惠北及团林站,由于相对湿度的增加和日照时数的减少,ET0表现出下降的趋势。

英文摘要：

Based on tens of years＂ meteorological data from three irrigation and drainage experimental stations, Beijing Changping, Kaifeng Huibei and Hubei Tuanlin, the daily reference evapotranspiration （ETo） is calculated by FAO Penman-Monteith equation. It is shown that the annual average value of daily ETo of Tuanlin station and Huibei station are decreasing with time, contrarily the value of Changping station is increasing. Through variation analysis of the synchronous meteorological data, we can conclude that these trends are due to the variation of climates factors, where the relative humidity plays a much important role,followed by the air temperature and sunshine hours. For Changping station, ETo has an increas- ing trend due to the decrease of relative humidity and the increase of wind speed; as to Huibei and Tuanlin Stations, ETo has a decreasing trend due to the increase of relative humidity and the decrease of sunshine hours.