Variations of pan evaporation and its attribution from 1961 to 2015 on the Loess Plateau, China

Whether the evaporation paradox exists or not is crucial for an improvement of water resource management on the Chinese Loess Plateau that has long been suffering from water scarcity. An in-depth understanding on long-term changes in evaporation and its attribution would be beneficial for a clear identification of evaporation paradox. However, the long-term and large-scale studies on evaporation variations were severely lacking on the Loess Plateau. This study examined both spatial and temporal variations in pan evaporation at 52 meteorological stations widespread on the Loess Plateau during 1961–2015. The Mann–Kendall test showed that significant decreases occurred in annual and seasonal pan evaporation ( p < 0.05). A principal component analysis indicated that regional-averaged annual pan evaporation experienced a decreasing trend in all three regions (the southwestern, southeastern and the northern regions of the Loess Plateau) with a decreasing rate ranging from −1.83 to −5.18 mm/a ( p < 0.05). The annual pan evaporation averaged across all the observations decreased significantly, whereas the average annual temperature increased, indicating the occurrence of a pan evaporation paradox on the Loess Plateau. Our results also showed that the pan evaporation was mostly sensitive to actual vapor pressure ( e a ), followed by solar radiation ( Rs ), mean temperature ( T mean ) and wind speed ( U 2 ). An increase in temperature resulted in an elevated pan evaporation; however, this was offset by an increase in vapor pressure and a decrease in wind speed and solar radiation. Wind speed was the dominant factor contributing to the pan evaporation decrease on the Loess Plateau. The results provided a useful reference for a more effective regional water resource management and ecological restoration.