Revisiting the Pan Evaporation Trend in China During 1988–2017
Jiaju Shen, Hanbo Yang, Sien Li, Ziwei Liu, Yongqiang Cao, Dawen Yang
Abstract
Abstract Pan evaporation decrease has been reported worldwide over the past decades. A recent increasing pan evaporation trend has been found globally. Remarkably, most studies on Chinese pan evaporation change were based on simulations involving meteorological variables, including temperature, radiation (sunshine duration [SSD]), wind speed, and relative humidity (RH), due to the pan evaporation observation inconsistency caused by the micro‐pan (D20) replacement with large pan (E601) around 2002. In addition, a large‐scale humidity sensor replacement across China occurred since the 2000s can cause an inconsistency of RH and in turn lead to that of simulated pan evaporation. Therefore, the recent pan evaporation trends independent of the observed RH in China should be revisited. In this study, we (a) generate merged D20 pan evaporation from 1988 to 2017 according to E601 observations under the constant conversion coefficient assumption between the evaporation observations of these pans in the same month of every year at each station, and (b) propose a framework based on the PenPan‐D20 model to attribute pan evaporation change into specific humidity (instead of RH or vapor pressure deficit in previous studies), SSD, air temperature, and wind speed, since RH and vapor pressure deficit are not independent from air temperature. The results show a significant 2.68 mm/a/a upward pan evaporation trend ( p < 0.05) across China from 1988 to 2017, which was primarily driven by the rising air temperature. Humidity sensor replacement causes an ∼2.2% inconsistency in RH, which produces nonnegligible errors in simulated pan evaporation trend.