| In this paper,the East China region is divided into three climatic regions by the cluster analysis,which are the northern region of East China,the middle region of East China and the southern region of East China.Based on the Pan evaporation and its related meteorological factors of 96 meteorological stations in East China during 1969 to 2018,Linear regression,Mann Kendall trend test,Sobol's sensitivity analysis and wavelet analysis theory are used to study the time trend,spatial distribution characteristics,influencing factors and periodic variation characteristics of Pan evaporation in the past 50 years in East China.The conclusions are as follows:The time trend of evaporation in East China is different from different perspectives.From the seasonal trend,the downward trend is mainly in summer.The evaporation in the north,middle,south of East China and the whole East China shows a significant downward trend in summer.The trend coefficients are-2.473mm/a,-1.119mm/a,-1.259mm/a and-1.46mm/a,respectively.In spring,autumn and winter,the evaporation of central,southern and the whole East China region shows a significant upward trend,but the trend coefficient is small,while the evaporation in the northern region of East China shows a significant downward trend in spring,autumn and winter.From the annual trend,theevaporation in the north of East China shows a significant downward trend,with the trend coefficient-5.473mm/a.The evaporation in the middle and south of East China shows an upward trend,with the trend coefficients 2.946mm/a and 2.579mm/a,respectively,which both passed the significance test.The spatial distribution of evaporation in East China shows the characteristics of more in north and south,less in the middle part.From the perspective of seasonal distribution,there is a significant difference between the north and the south in spring,with the Yangtze River Basin as the boundary,showing the characteristics of more in the north and less in the south.The difference between the north and the south in summer is not significant,and the distribution of the evaporation in autumn and winter is consistent,the higher evaporation only presenting in the north and the south.In the four seasons,the trend of each station is different.The number of stations with rising evaporation in spring,summer,autumn and winter accounts for 56%,26%,37.5% and 33.3% of the total.The sensitivity of main influencing factors of evaporation with descending order in the north of East China are relative humidity,average wind speed and solar radiation;the main influencing factors of evaporation in different seasons in the middle of East China are different,among which the main sensitive factor of evaporation in spring,autumn and winter is relative humidity,the secondary sensitive factors are solarradiation and average wind speed;while the main sensitive factors of evaporation in summer is solar radiation,and then is relative humidity.The main influencing factors in the south of East China are relative humidity>solar radiation>average wind speed.The main periods of seasonal evaporation in the north,the middle and the south of East China are 2?6a,2?4a and 2?3a,respectively.From the perspective of East China as a whole,the main period of seasonal evaporation is 2?4a.From the perspective of annual evaporation,the main period of evaporation is 2a in the north and south of East China,4a in the middle of East China and 8a in East China.In the influencing factors of evaporation,the phase of relative humidity and evaporation is reverse,showing significant negative correlation;the phase of solar radiation and evaporation is in the same direction,showing significant positive correlation;both of them are highly correlated with the evaporation,with resonance period on the scale of 0?4a and 6?10a,and the impact on evaporation is continuous;the change of average wind speed and evaporation is in the same phase,with weak correlation intensity,and the resonance period with evaporation is mainly mainly on the scale of 4 ? 8a. |
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