Abstract: Reference crop evapotranspiration(ET0)was a key factor to calculate crop water requirement and a main parameter to forecast real irrigation amount.The characteristics of ET0and its major climate influence factors were analyzed by using Morlet wavelet analysis,M-K abrupt change testing and correlation analysis method,based on surface meteorological data of 11 stations in Hengshui from 1981 to 2010.The main results showed that the annual ET0 decreased fluctuant,and the decline rate was significant.The monthly ET0 was declined,except for February and March.The annual ET0 in the northeast Hengshui was larger than that of the southwest.The larger annual ET0，the more annual ET0 declined,and vice versa.The annual ET0 had a significant quasi 6 years oscillation period.High consistency was the main spatial characteristic about annual nd monthly ET0.Diurnal temperature range,maximum temperature,sunshine duration and relative humidity were the most important meteorological factors that affected the ET0,and the degree of their influence changed with the season.There was significant positive correlation between ET0 and diurnal temperature range and maximum temperature and sunshine duration,and negative correlation between ET0 and relative humidity.While the effect of wind speed on E0 was weak.Among all the factors which had significant influences on the ET0 from May to September,sunshine duration had the most prominent impact,diurnal temperature range,relative humidity and maximum temperature also had evident influences on the ET0.

Key words: Reference crop evapotranspiration(ET0), Penman-Monteith equation, Spatial and temporal variation, Climate causes, Hengshui