Bivariate attribution of the compound hot and dry summer of 2022 on the Tibetan Plateau

Abstract

The extraordinarily high temperatures experienced during the summer of 2022 on the Tibetan Plateau (TP) demand attention when compared with its typical climatic conditions. The absence of precipitation alongside the elevated temperatures resulted in 2022 being the hottest and driest summer on record on the TP since at least 1961. Recognizing the susceptibility of the TP to climate change, this study employed large-ensemble simulations from the HadGEM3-A-N216 attribution system, together with a copula-based joint probability distribution, to investigate the influence of anthropogenic forcing, primarily global greenhouse gas emissions, on this unprecedented compound hot and dry event (CHDE). Findings revealed that the return period for the 2022 CHDE on the TP exceeds 4000 years, as determined from the fitted joint distributions derived using observational data spanning 1961–2022. This CHDE was directly linked to large-scale circulation anomalies, including the control of equivalent-barotropic high-pressure anomalies and the northward displacement of the subtropical westerly jet stream. Moreover, anthropogenic forcing has, to some extent, promoted the surface warming and increased variability in precipitation on the TP in summer, establishing conditions conducive for the 2022 CHDE from a long-term climate change perspective. The return period for a 2022-like CHDE on the TP was estimated to be approximately 283 years (142–613 years) by the large ensemble forced by both anthropogenic activities and natural factors. Contrastingly, ensemble simulations driven solely by natural forcing indicated that the likelihood of occurrence of a 2022-like CHDE was almost negligible. These outcomes underscore that the contribution of anthropogenic forcing to the probability of a 2022-like CHDE was 100%, implying that without anthropogenically induced global warming, a comparable CHDE akin to that observed in 2022 on the TP would not be possible.