Anthropogenic influences on 2022-like summer heatwaves over the Yangtze River valley and projected changes in the likelihood of the event

Abstract During summer 2022, a record-breaking heatwave occurred in China over the Sichuan Basin to the middle and lower reaches of the Yangtze River valley. Observational analysis shows that this heatwave event peaks around 17th August, with an anomaly of 10 day running mean Tmax anomalies (TXa10day) being equal to 4.15 °C, which is 4 times the interannual standard deviation. This event is too rare in both observations and model simulations during the historical period 1961–2022 to make robust attribution statements. Therefore, we focus on a 2022-like summer heatwave event, defined as a 1-in-100-year event with a TXa10day anomaly of 3.19 °C based on observations during 1961–2022. Based on the multi-model ensembles of the sixth Coupled Model Intercomparison Project (CMIP6), we find that anthropogenic forcings lead to an increased likelihood of a 2022-like summer heatwave event by about 3 times in the present climate (2018–2027), with greenhouse gas forcing enhancing the likelihood of this event and aerosol forcing reducing the likelihood of this event. This increase in likelihood corresponds to a change of return period from 1-in-53-year event under natural forcing to 1-in-17-year event under all forcing in the present climate. Climate model projections show that a 2022-like summer heatwave event will become more frequent in a warmer climate with the likelihood of such event increasing exponentially with increasing global warming level (GWL). Such an extreme event will become a 1-in-8.4-year, 1-in-5-year, 1-in-2-year and 1-in-1.3-year event under the SSP5-8.5 at the 1.5 °C, 2 °C, 3 °C and 4 °C GWLs compared with the present climate. These results suggest that China would face a challenge to take adaptation measures to cope with the projected frequency increase of the 2022-like summer heatwave.