Sensitivity analysis of reference crop evapotranspiration in Anhui province in the recent 40 years

Using the FAO Penman-Monteith equation to calculate ET0 based on daily meteorological data collected from 79 meteorological stations from 1971 to 2010 in Anhui Province,quantitative analysis had been done on temporal and spatial distribution characteristics as well as influencing factors of ET0 respectively.The results showed that average yearly ET0 was 862 mm and with a trend of fluctuate-decrease since 1971.Generally,it decreased from the northeast to the southwest,which was higher in plain,and lower in mountain.As for analysis of sensitivity coefficient,the largest factor contribution to the change of ET 0 was relative humidity,the second were sunshine hours and wind speed,the minimum was average temperature.In recent 40 years,the yearly change trends of sensitivity coefficient of average temperature,sunshine hours and wind speed were not obvious and presented smooth fluctuation,while the change trends of sensitive coefficient of relative humidity showed a clear upward trend(α=0.01).its absolute value decreased,indicating that the relative humidity sensitivity of ET 0 in weakening trend.In the annual change characteristics,sensitive coefficient variation of relative humidity showed obvious double peak characteristics,while the annual change characteristics of the average temperature,sunshine hours and wind speed showed single peak.Concerning to contribution of main factors to ET 0,the largest one was relative humidity,total contribution of four main factors to ET 0 was-1.33,and the change of sunshine hours and wind speed largely explained the decrease trend of ET 0.