Negative trends in measured pan evaporation have been widely reported. No consensus has been reached about the underlying causes of natural changes in pan evaporation. A physically based estimate of pan evaporation in a nature reserve should be useful in understanding regional climate change. 

Prof. Zhang Yiping and his research team of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study at a site in Ailaoshan Nature Reserve (24°32′N, 101°01′E; 2480 m a.s.l.) in south-west China. Their objectives were to answer the following questions: (1) what changes in pan evaporation are occurring in the nature reserve? (2) What are the main factors contributing to these changes in pan evaporation?

　Their study has shown a positive trend in pan evaporation, contrary to the widely reported reduction in pan evaporation. Their result is consistent with the increase in potential evaporation reported in south-west China.

Their results showed that change of wind speed had contributed most of the change in pan evaporation, followed by sunshine hours. In terms of seasonal patterns, the change of the aerodynamic component was dominant over the change of pan evaporationin the dry season, and the change of the radiative component was dominant over the change of pan evaporation in the wet season. Consequently, water evaporation demand could be predicted more efficiently based on the current trends of climatic variables.

The study entitled “On the attribution of changing pan evaporation in a nature reserve in SW China” has been published online in Hydrological Processes, DOI: 10.1002/hyp.9394