Impact of global dimming on reference evapotranspiration in Hai River basin, China

Abstract. Global radiation can impact the surface energy balance and hydrological cycle. This study analysed changes in global radiation in Hai River basin, China during 1960 to 2012. Global radiation decreased significantly from 1960 to 1989 and increased from 1990 to 2012, which has been described as “from dimming to brightening”. Sunshine duration was used as a proxy index where radiation records were unavailable. Results showed that sunshine duration (for 45 stations) show a significant decreasing trend from 1960 to 2012, which was a little different to global radiation (for 6 stations) during the brightening phase. Penman-Monteith model was used for estimating trends of reference evapotranspiration. The consistency of temporal and spatial variations in sunshine duration and reference evapotranspiration was examined during the periods 1960−1989 and 1990−2012. The results showed that the annual reference evapotranspiration trend was consistent with the sunshine duration trend (both were decreasing for 37 of the 45 stations) during 1960 to 1989, followed by an upward trend (for 26 of the 45 stations) from 1990, while the annual sunshine duration indicated a downward trend (for all 45 stations) during the whole period 1960−2012. Overall, global dimming could be the dominant factor for the decreased reference evapotranspiration from 1960 to 1989, while the increased reference evapotranspiration from 1990 to 2012 could be driven by other meteorological variables, especially global warming.