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

Abstract

Long-term variability of direct and diffuse solar radiation (Rdir and Rdif) is essential for climate change study. However, Rdir and Rdif observations suffer from low spatiotemporal coverage and inhomogeneity. This study improved hybrid models to calculate Rdir and Rdif from sunshine duration and meteorological data at ~2,000 stations from 1958 to 2017 over China and demonstrated their reliability. We identified that Rdir 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 Rdir and Rdif were also revealed. From 1958 to 1989, our results show that Rdir displays a significant downtrend (−3.52 W m−2 per decade), whereas Rdif shows a significant increasing trend (0.84 W m−2 per decade), especially over the North China Plain. From 1990 to 2017, Rdir decreases nonsignificantly by −0.47 W m−2 per decade but Rdif shows a slight decline of −0.28 W m−2 per decade.