Periodic fluctuation of reference evapotranspiration during the past five decades: Does Evaporation Paradox really exist in China?

Evidence that the pan evaporation or reference evapotranspiration (ET) as the indicator of atmospheric evaporation capability have decreased along with the continuous increase in temperature over the past decades (coined as "evaporation paradox") has been reported worldwide. Here, we provide a nationwide investigation of spatiotemporal change of ET using meteorological data from 602 stations with the updated data (1961-2011). In addition, we explore the trigger mechanism by quantitative assessment on the contribution of climatic factors to ET change based on a differential equation method. In despite of different shift points regionally, our results suggest that the ET generally present decadal variations rather than monotonic response to climate change reported in previous studies. The significant decrease in net radiation dominate the decrease in ET before early 1990s in southern regions, while observed near-surface wind speed is the primary contributor to the variations of ET for the rest regions during the same periods. The enhancements of atmospheric evaporation capability after early 1990s are driven primarily by recent relative humidity limitation in China. From a continental scale view, as highly correlating with to Pacific Decadal Oscillation, the shift behaviors of ET is likely an episodic phenomenon of the ocean-atmosphere interaction in earth.