Long-Term Trends of Estimated Surface Incident Shortwave Radiation in China During 1970–2015

Surface incident shortwave radiation (Rs) is an important factor of the environment system. Knowledge of the Rs variations is important for studying the hydrological cycle and climate change. Although ground measurements provide accurate Rs data, insufficient observations limit their application for analyzing the variations of the Rs. In this study, long-term trends of the Rs over China were analyzed based on the newly reconstructed Rs data. First, the Random Forest (RF) method was used to develop the Rs estimation model using ground-measured radiation data and meteorological data from the Climate Data Center of the Chinese Meteorological Administration (CDC/CMA); then, the RF-based model was further applied to extend the Rs data at 454 CDC/CMA meteorological stations during 1970-2015; finally, the trends in Rs across China were analyzed using the Mann-Kendall (M-K) test method. The evaluation results of the RF-based model showed that the overall correlation coefficient (R) value was 0.96, the bias value was 0.06 (0.04%) Wm- 2 , and the root mean square errors (RMSE) value was 23.92 (14.83%) Wm- 2 . A significant decrease trend of the Rs in China with the average decrease of 1.1 (0.68%) Wm- 2 per decade showed up between 1970 and 2015. Additionally, a recovery trend of the Rs in China with the average increase of 0.4 (0.25%) Wm- 2 per decade was observed during 1989–2015.