Pan evaporation paradox and evaporative demand from the past to the future over China: a review

Abstract

In a warming climate, there was a long‐term expectation that the atmospheric evaporative demand would increase, which was challenged by an unexpected discovery two decades ago of decreases in measured pan evaporation, now widely termed as the ‘pan evaporation paradox.’ In this review, we summarize recent reports on the pan evaporation paradox around the world over the past half century, possible causes, implications for the water cycle, and its possible change in the future. We then present a case study of China based on the latest meteorological datasets and the state‐of‐the‐art General Circulation Models (GCMs). We confirm that pan evaporation (Epan) decreases in most parts of China at an average of about −2.60 mm/y2, and this decrease disappears around 1993. We introduce and develop a detrending approach in sensitivity analysis and find that changes in solar radiation, wind speed, and relative humidity overcompensate the positive contribution of increasing air temperature in Epan and lead to the well‐known pan evaporation paradox. Positive changes in Epan using 12 state‐of‐the‐art GCMs for 2021–2050 and for 2071–2100 under RCP4.5 and RCP8.5 scenarios, respectively, when compared with their corresponding multiyear mean over 1971–2000 as base line, shows that the evaporation paradox would not appear in the future. We highlight that it is vital and promising to move forward to interpreting how the atmospheric evaporative demand would change in the future. WIREs Water 2017, 4:e1207. doi: 10.1002/wat2.1207This article is categorized under: Science of Water > Hydrological Processes Science of Water > Water and Environmental Change