Quantitative Analysis of Climate Factors for Potential Evapotranspiration Changes in Shandong

Based on the daily data from 1961 to 2010 of 90 meteorological stations in Shandong Province,the changes of potential evapotranspiration(ET0) were studied by analyzing the sensitivity coefficients of ET0 to average wind speed,relative humidity,sunshine duration,daily maximum temperature and daily minimum temperature together with the relative changes of these climate factors by using the Penman-Monteith method recommended by FAO.The results showed that the annual ET0 was decreasing with the speed of-1.818 mm/a,and it is more significant in summer.The mutation of annual ET0 happened around 1983 and the annual ET0 increased indistinctly after that.The influence of average wind speed on the changes of ET0 was greater in northwest Shandong and was less in the coastal area.The influence of average relative humidity on the changes of ET0 was larger in the peninsula and was less in the middle mountain area.The influence of sunshine duration on the changes of ET0 was greater in southwest Shandong and south Shandong.The influence of maximum temperature on the changes of ET0 was greater in southwest Shandong,west Shandong,and north Shandong.The correlation between climate factors and the changes of ET0 was significantly different in space.The changes of ET0 was primarily attributed to the wind speed due to its significant trends of decreasing,and followed by sunshine duration.The maximum temperature and the minimum temperature had a little positive contribution to the change of ET0.The positive contribution of relative humidity was greater in the coastal area.The main impacting factor was the wind speed generally in a whole year,and it was so in spring,autumn and winter,but it was sunshine duration in summer.However the peninsula is an exception,that the relative humidity was always the main factor.The sites dominated by the wind speed reduced obviously after the mutation,but that dominated by the relative humidity increased evidently.Because of the significant decrease of sunshine duration in summer,the main impacting factor in summer was sunshine duration in most areas after the mutation.