Abstract: Based on the climatic data of 85 meteorologica stations in Hebei Province in 1965-1999,the temporal and spatial variation of the reference evapotranspiration and its relationship to the climate change by using the FAO Penman-Monteith equation were analyzed.The results showed that the annual and four seasons' reference evapotranspiration in Hebei Province significantly declined(α=0.01).The reference evapotranspiration quickest declined in spring and then in summer,while it slowly declined in autumn and slowest in winter.The decline rate of the mean annual of the reference evapotranspiration was by 43.58mm per ten years.The spatial distribution of the decreasing extent of the reference evapotranspiration was different in the different regions in Hebei Province.It had a remarkable decline in Langfang areas and the South of Langfang areas with the reducing rate above 40mm per ten years,while it slightly declined in the North parts of Hebei Province with 35mm per ten years.The reference evapotranspiration not significantly declined in Qinhuangdao areas.The results of correlation analysis between the reference evapotranspiration and meteorological factors showed that the drops of wind speed and sunshine hours were founded to be the most important meteorological factors which affected reference evapotranspiration variation trends in Hebei Province,while the air temperature increase had not significant effect on the references evapotranspiration change.

Key words: References evapotranspiration, References evapotranspiration, Temporal and spatial variations, Penman-Monteith equation, Climate change