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 ~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.