Spatio-temporal variation characteristics of photosynthetically Active Radiation in China in recent 50 years

Based on long-term measurement data of weather/ecological stations over China, we calculate and produce mean annual/seasonal Photosynthetically Active Radiation (PAR) spatial data from 1961 to 2007, using climatological calculation and spatialization technique. And we analyze the spatio-temporal variation characteristics of mean annual/seasonal PAR spatial data in China in recent 50 years, by means of Mann-Kendall trend analysis method and GIS spatial analysis technique. The results show: (1) As a whole, the spatial distribution of PAR differs significantly across China, with lower PAR in the eastern and southern parts of China and higher PAR in the western part. Mean annual PAR over China ranges from 17.7 mol m^-2 d^-1 to 39.5 mol m^-2 d^-1. (2) Mean annual/seasonal PAR of every pixel over China is averaged and the mean value declines visibly with a fluctuant process, and the changing rate of mean annual PAR is -0.138 mol m^-2 d ^-1/10a. The extents of change in different seasons are different, with the maximum dropping in summer. (3) The analysis by each pixel shows that PAR declines significantly (α= 0.05) in most parts of China. The changing trend in the eastern part is more obvious than that in the western part, and summer and winter play more important roles in the interannual variability of PAR. North China is always a decreasing zone in four seasons, while the northwest of Qinghai-Tibet Plateau turns to be an increasing zone in four seasons. (4) The spatial distributions of the interannual variability of PAR in different periods are not the same. The interannual variability of PAR" in a certain region is not only different among four seasons, but also different among different periods.