Variability in Direct and Diffuse Solar Radiation Across China From 1958 to 2017

Long-term variability of direct and diffuse solar radiation (R-dir and R-dif) is essential for climate change study. However, R-dir and R-dif observations suffer from low spatiotemporal coverage and inhomogeneity. This study improved hybrid models to calculate R-dir and R-dif from sunshine duration and meteorological data at similar to 2,000 stations from 1958 to 2017 over China and demonstrated their reliability. We identified that R-dir observations show a spurious steep downtrend before 1990 due to the sensitivity drift of the measuring instruments, implying an overestimation of global dimming. Long-term trends and spatiotemporal details in R-dir and R-dif were also revealed. From 1958 to 1989, our results show that R-dir displays a significant downtrend (-3.52 W m(-2) per decade), whereas R-dif shows a significant increasing trend (0.84 W m(-2) per decade), especially over the North China Plain. From 1990 to 2017, R-dir decreases nonsignificantly by -0.47 W m(-2) per decade but R-dif shows a slight decline of -0.28 W m(-2) per decade.