Abstract/Summary

Heatwaves (HWs) are weather events characterized by extreme hot surface air temperature anomalies that persist for several days. This thesis aims to understand the drivers and physical processes of HW changes over different parts of China during the recent decades and their projected changes in the future at different global warming levels (GWLs). In the recent decades (1995-2020), Compound (hot in day and night) and Nighttime HWs across China and Daytime HWs over central China have increased significantly compared with the period 1961-1994, which is mainly due to increases in seasonal mean warming. The increases of HW properties are predominantly explained by external forcing changes in which greenhouse gas changes play a dominant role and aerosol changes lead to a weak increase (decrease) over Northern (Southern) China. Climate model projections point to a future in which China faces an increased frequency, enhanced intensity and extended duration of Compound HWs. Overall, seasonal mean warming dominates HW property changes and it is related to an increase of downward longwave radiation and increase of shortwave radiation (under SSP5-8.5) over eastern China. Shortwave radiation changes tend to play a weaker role for surface warming under SSP3- 7.0 than under SSP5-8.5, due to greater aerosol changes under SSP3-7.0. Moreover, there is a considerable model spread in the projected HW property changes with the water vapor feedback and shortwave cloud radiative effect being two important factors. During summer 2022, a record-breaking heatwave occurred over eastern China. The anthropogenic influences and the likely future changes of a similar event are assessed using climate model simulations. Anthropogenic forcings have increased likelihood of the 2022- like summer heatwave event by about 3 times relative to the world with natural forcings. Climate model projections show that the likelihood of such an extreme event over eastern China increases exponentially with increasing GWL.