资源环境科技发展态势分析平台

The aim of this study was to reveal the long-term variation properties of photosynthetically active radiation (PAR) over China. A series of reliable empirical PAR estimation equations suitable for all-sky conditions were developed using data measured in situ from 2005 to 2014, which were obtained from the Chinese Ecosystem Research Network (CERN). These equations were then combined with a hybrid model to reconstruct the PAR from 1961 to 2014 for 724 weather stations belonging to the China Meteorological Administration (CMA). There was a decreasing linear trend in the PAR (with an amplitude of -0.009molm(-2) day(-1) year(-1)) from 1961 to 1981 and a steady low level of -0.003molm(-2) day(-1) year(-1) during 1981-2014 for all of China. The PAR over the Tibetan Plateau (TP) region increased from 1961 to 1984; then, this linear trend slightly changed. The breakpoint years for the northwest China (NWC), southwest China (SWC), north China (NC), northeast China (NEC) and east China (EC) regions were 1985, 1981, 1996, 1998 and 1979, respectively. In addition, the aerosol optical depth, ozone column concentration, cloud cover and water vapour content attenuated the PAR that would otherwise have reached the earth's surface by approximately 7.59, 1.12, 18.13 and 6.20%, respectively.