Causes of the extremely low solar radiation in the 2021 growing season over southeastern Tibetan Plateau and its impact on vegetation growth

The Tibetan Plateau (TP), known as the ‘Third Pole’ region, is one of the most sensitive places to global climate change, which possesses the highest surface incident solar radiation (SSR) in China. In the 2021 growing season, i.e., May to September, southeastern Tibetan Plateau (SETP) registered a widespread and extremely low SSR since 1950 with approximately -18.65 W/m² of regional mean anomaly relative to 1950-1979 mean. Through the analyses using observations, reanalysis and CMIP6 model simulations, the extremely low SSR event in 2021 is mainly attributed to more clouds and abundant atmospheric moisture caused by anomalous southerlies from the Bay of Bengal. The existence of abnormal south winds could increase the probability ratio of such low SSR events like 2021 to be 9.25 (95% CI: 6.56-19.02). Anthropogenic aerosols and GHGs-induced warming might increase the probability of such SSR events to be a factor of 4.70 (95% CI: 1.66-15.49) and 1.66 (95% CI: 1.01-6.59), respectively. As a result, the extremely low SSR event could significantly reduce local gross primary productivity in the 2021 growing season over SETP, especially in the humid eastern SETP where SSR has a stronger impact on vegetation photosynthesis.