Abstract
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.
Highlights
Global radiation, the sum of direct radiation and diffuse radiation, is the fundamental energy source for life and the main driving factor of land surface processes, such as evaporation, plant photosynthesis and snow melt
To estimate temporal and spatial variations over the whole region, sunshine duration is used as the proxy for solar radiation
The consistency of temporal and spatial variations in sunshine duration and reference evapotranspiration was examined during the periods 1960−1989 and 1990−2012
Summary
The sum of direct radiation and diffuse radiation, is the fundamental energy source for life and the main driving factor of land surface processes, such as evaporation, plant photosynthesis and snow melt. Many recent studies using solar radiation records updated to the year 2000 have found a reverse trend named “brightening” since the 1980s (Wild et al, 2005). The surface radiation balance is the principal driver of the global hydrological cycle (Wild and Liepert, 2010), and the connecting term between the water and energy balance is evapotranspiration. Previous studies based on qualitative analysis found that the decrease of global radiation may be the best explanation of the evaporation paradox (Teuling et al, 2009; Papaioannou et al, 2011; Matsoukas et al, 2011; Zhang et al, 2012), but further quantitative proof is needed
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