Assessing contributions to panevaporation trends in Haihe River Basin, China

In many places around the world, panevaporation has been detected to decrease with the increase in temperature, which is known as the "panevaporation paradox.'' An example of the paradox was found in the Haihe River Basin from 1957 to 2001. To explain the mechanism of the paradox, an approach to quantify the contributions of climate factors to the panevaporation trend has been proposed, in which the individual contribution was defined as the product of the partial derivative and slope of the trend for the concerned variables. Four variables, including temperature, wind speed, solar radiation, and vapor pressure, were selected based on the Penman-Monteith method to assess their individual contribution to the panevaporation trend. The results showed that an increase in temperature resulted in the increase of panevaporation, but this effect had been offset by an increase in vapor pressure and decrease in wind speed and solar radiation. Wind speed was the dominant factor contributing to panevaporation decreases in the Haihe River Basin.