Spatiotemporal Variations of Top-of-Atmosphere Radiation Components over the Tibetan Plateau During the Past Four Decades

The Tibetan Plateau (TP) plays a crucial role in the global climate system, yet long-term trends in its top-of-atmosphere (TOA) radiation budget remain poorly understood. Using 40-year (1981–2020) CLARA-A3 satellite data and reanalysis datasets, we quantify the spatiotemporal variations of TOA reflected shortwave radiation (RSF) and outgoing longwave radiation (OLR), and decompose the RSF into atmospheric and surface contributions. Additionally, we attribute observed trends to key drivers via multiple linear regression. The TP shows a significant decrease in RSF (−11.06 W/m2) and a significant increase in OLR (+4.88 W/m2). Spatially, OLR increases are widespread and statistically significant over the central and western plateau, while RSF trends are heterogeneous and mostly non-significant except for localized negative trends. The atmospheric contribution to RSF declines markedly (−0.329 W/(m2·year)), whereas the surface contribution increases (+0.061 W/(m2·year)). Attribution analysis identifies cloud fraction change (CFC) as the dominant drivers: it explains most of the RSF decline and the OLR increase. Cloud optical thickness and vertical structure play only minor roles. Our findings demonstrate that decreasing cloud cover is reshaping the TP’s TOA energy budget, providing essential geo-information for the spatial evaluation of climate models and the refinement of satellite-derived radiation products.