Analysis on Change of Reference Crop Evapotranspiration and Climatic Influence Factors in Sichuan

Reference crop evapotranspiration(ET0) was a key factor to estimate crop water requirement and determine farming irrigation.The characteristics of ET0 and its major climate influence factors were analyzed respectively by using the Penman-Monteith equation and partia1 correlation analysis method,based on daily meteorological data from 5 basin stations and 5 plateau stations from 1961 to 2009 in Sichuan province.The results showed that both daily and monthly average ET0,both in basin stations and plateau stations,changed in seasons.The highest point was in summer,and the lowest point was in winter.The annual average ET0 in basin stations decreased fluctuant,and the decline rate was significant.The annua1 average ET0 in plateau stations decreased slightly except for Muli and Songpan.The annual and seasonal average ET0 in Sichuan province had close relationship to sunshine duration,wind speed,relative humidity,average temperature,maximum and minimum temperature,and air pressure.Sunshine duration reduction in last 50 years resulted to average ET0 decreased in basin stations,and the wind speed varation resulted to average ET0 decreased in plateau stations.