Detection and Attribution of Changes in Summer Compound Hot and Dry Events over Northeastern China with CMIP6 Models

Northeastern China has experienced a significant increase in summer compound hot and dry events(CHDEs),posing a threat to local agricultural production and sustainable development.This study investigates the detectable anthropogenic signal in the long-term trend of CHDE and quantifies the contribution of different external forcings.A probability-based index(PI)is constructed through the joint probability distribution to measure the severity of CHDE,with lower values representing more severe cases.Response of CHDE to external forcing was assessed with simulations from the Coupled Model Intercomparison Project phase 6(CMIP6).The results show a significant increase in the severity of CHDE over northeastern China during the past decades.The trend of regional averaged PI is-0.28(90%confidence interval:-0.43 to-0.13)per 54 yr and it is well reproduced in the historical forcing simulations.The attribution method of optimal fingerprinting was firstly applied to a two-signal configuration with anthropogenic forcing and natural forcing;the anthropogenic impact was robustly detected and it explains most of the observed trend of PI.Similarly,three-signal analysis further demonstrated that the anthropogenic greenhouse gases dominantly contribute to the observed change,while the anthropogenic aerosol and natural forcing have almost no contribution to the observed changes.For a compound event concurrently exceeding the 95 th percentile of surface air temperature and precipitation reversal in the current period,its likelihood exhibits little change at 1.5℃global warming,but almost doubled at 2.0℃global warming.

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

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.