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 95th percentile of surface air temperature and precipitation reversal in the current period, its likelihood exhibits little change at 1.5°C global warming, but almost doubled at 2.0°C global warming.