Abstract: Based on the daily data of mean temperature,maximum temperature,minimum temperature,relative humidity,wind velocity,sunshine hours and atmospheric pressure from 1957 to 2009 on five weather stations-Wuqiang,Shenze,Raoyang,Jinzhou and Xianxian in Heilonggang basin,the reference crop evapotranspiration of each station for different time scales was estimated by Penman-Monteith method.The change trend of ET0was analyzed by linear trend analysis method,and the fractal characteristics of time series for ET0 in the basin was studied by sliding R/S analysis method.The linear trend analysis indicated that the climate tendency ratio of annual ET0of every station over the years in the history since 1957 was between-33.81～-10.79 mm per 10 years,which all were in a decreasing trend,but presented great difference between each station;the monthly climate tendency ratio was between-11.27～2.02 mm per 10 years,most of it was under 0,the lowest monthly climate tendency ratio was in May and June in each station;the climate tendency ratio of each season was between-15.87～1.3 mm per 10 years,the ratio was the difference between each station in summer,and there was the maximum difference between Raoyang and other stations in summer.The comparative analysis of climate tendency ratio for meteorological factors showed the main reason which resulted in the decreasing trend of ET0 in the basin were the decreasing of wind speed and sunshine hours,and the increasing of daily maximum and minimum temperature;the main reason which resulted in the evident decreasing trend of ET0 in May and June were the decreasing of wind speed and sunshine hours,the slower increasing of daily mean temperature,and the evident increasing of relative humidity;the main reason which resulted in great difference between Raoyang and other four stations for ET0 change trend were the slower decreasing of wind speed and sunshine hours,the slower increasing of daily maximum and minimum temperature,the evident decreasing of relative humidity and atmospheric pressure in February,March,November and December,which causing the increasing trend of monthly ET0 in these months and the slower decreasing trend of annual ET0.The result of R/S analysis showed that over the year and in each season,the Hurst indexes in each station were greater than 0.5,the correlation coefficient were greater than 0.98,and the fractal dimensions were less than 1.5.This suggested that the time series for ET0 of the year and each season have a sustainability,ET0 in the future would decrease,and the decreasing trend also exists in monthly ET0 in other stations except for Raoyang.

Key words: Heilonggang basin, Heilonggang basin, Reference crop evapotranspiration, Time series, Climate tendency ratio, Fractal features