The unignorable impacts of pan wall on pan evaporation dynamics

Open water evaporation (E-ow), such as evaporation of lake and reservoir, is typically estimated by observations of different pans. The observation networks of pan evaporation (E-pan) were established and maintained worldwide for a long history. All the pans in the world consist of water body and pan wall, which includes side wall, pan rim and (if any) pan bottom. Since the pan wall will affect E-pan by radiation absorption and heat conduction, once pan wall absorbs and conducts more heat for vaporizing than water body in a pan, observed E-pan dynamics will greatly deviate E-ow causing uncertainties and errors in estimating E-ow. Thus, this study calculated E-pan at 767 meteorological stations in China and quantified the contributions of water body and pan wall on E-pan trends. For China as a whole, E-pan decreased at -3.75 mm/a(2) and increased at 3.68 mm/a(2) during 1960-1993 and 1993-2016, respectively. 84% of E-pan trends were contributed by water body. For 767 stations, E-pan trends of 84 and 96 stations were dominated by pan wall during 1960-1993 and 1993-2016, respectively. Since pan wall contributed more than half of E-pan trends for (similar to)23% of the stations in China, the impacts of pan wall on E-pan dynamics cannot be ignored.