Spatio-temporal Variation Characteristics of Surface Net Radiation in China over the Past 50 Years

Abstract

Surface net radiation is the sum of incident downward and upward shortwave and longwave radiation.Changes of surface net radiation control the Earth's climate,the hydrological cycle,and plant productivity.In this paper we focused on the spatio-temporal variation analysis of surface net radiation over China at site-scale.We estimated the parameters of the FAO Penman model using daily surface net radiation of 53 radiation sites during1993-2010 over China,and then we calculated mean annual/seasonal surface net radiation data in 699 weather sites from 1961-2010,based on the model and long-term measurement data of these stations.Furthermore,we analyzed the spatio-temporal variation characteristics of mean annual/seasonal surface net radiation of 699 sites in China in recent 50 years,by means of Mann-Kendall trend analysis method and GIS spatial analysis technique.We concluded that: 1) Parameterization of the FAO Penman model shows that the model has a relatively high simulation accuracy with RMSE 27.9W/m2,the coefficient of correlation 0.85,and the mean relative error 13%;2) Mean annual/seasonal surface net radiation over China declines visibly with a fluctuant process with the changing rate reaching 0.74 W/m2 every 10 years.The amplitudes of changes vary with the seasons with the maximum downtrend(1.93 W/m2 every 10 years) in summer;3) The analysis at each site shows that mean annual surface net radiation declines significantly(α=0.05) in most sites(59.8%).The changing trend of the eastern part is more obvious than that in the western part and summer plays the most important role in the interannual variability of surface net radiation.Northern China,Central China and Southern China are decreasing regions in spring,summer and autumn,while the Qinghai-Tibet Plateau turns to be a noticeable decreasing zone in winter.We speculated the much heavier aerosol loading in eastern part of China should be the primary cause for the decrease in surface net radiation and the volcano aerosols contribute to the oscillation in the trend.The increasing trend of snow on the Qinghai-Tibet Plateau should account for the decreasing trend of surface net radiation in winter.The quantitative spatio-temporal analysis of surface net radiation will be vital for the climate change and terrestrial ecosystem evapotranspiration research.