Characteristics And Causes Of Panevaporation Over Eastern China In Recent 40 Years

In many places around the world,panevaporation(E_pan)has been detected to decrease with the increase in temperature,which is known as the“panevaporation paradox”.Based on the Ensemble Empirical Mode Decomposition?EEMD?and the Empirical Orthogonal Function?EOF?,the spatio-temporal characteristics of panevaporation over Eastern China in resent 40 years.The results show that panevaporation significantly decreased with the rate of decrease is-5.21mm/yr in Eastern China using the observed panevaporation records for the period 1970-1993.However,the observed panevaporation has significantly increased for the period1993-2013 by 7.7 mm/yr.To explain the mechanism of the long-term panevaporation trend,an approach to quantify the contributions of climate factors to the long-term panevaporation trend has been proposed,in which the individual contribution was defined as the product of the partial derivative and the slope of the trend for the concerned variables.Four variables,including relative humidity,solar radiation,temperature and wind speed,were selected based on the Penman-Monteith method to assess their individual contribution to the long-term panevaporation trend.The results showed that an increase in temperature and a decrease in relative humidity resulted in the increase of panevaporation,but this effect had been offset by a decrease in solar radiation and wind speed.Solar radiation was the dominant factor contributing to panevaporation decreases in Eastern China for the period 1970-1993.However,the amplitude of decrease in relative humidity,while the amplitude of decrease in wind speed and solar radiation for the period 1994-2013.The results show that decreasing significantly relative humidity dominated the change in the long-term panevaporation trend,which offset the effect of wind speed and solar radiation,then led to the increase in the long-term panevaporation trend.