Change in the heatwave statistical characteristics over China during the climate warming slowdown.

Heatwaves are multi-day periods of extremely high-temperature weather relative to a region's average conditions and are among the deadliest natural disasters. This study was designed to evaluate changes in the characteristics of heatwaves during the periods of warming acceleration versus warming slowdown using the multivariate joint probability distributions of heatwave duration and severity. The results revealed that: (1) From the warming acceleration period (1961–1997) to the warming slowdown period (1998–2017), the return levels of heatwave duration increased by <1.0 d as the return period increased. As the return period lengthened, the return level of heatwave severity rose as well; (2) The joint occurrence probability of heatwaves with both variables exceeding the 20-yr, 50-yr, and 100-yr return levels exhibited relative increases of 3%, 8%, and 16% across China, respectively. There were greater than the joint probability of heatwaves with only 1 variable exceeding the return levels; (3) The number of heatwaves with both duration and severity exceeding the 50-yr joint return period increased in China, and this increase was dominated by heatwaves with joint return periods of 50–100 years, leading to a strengthening of heatwave severity. • The Copula function was used to connect the duration and severity of heatwaves; • The return level of heatwave severity rose more significantly than duration in China; • The probability of heatwaves with both variables exceeding the 100-yr return level exhibited a increase of 16% in China; • The increase of the joint probability of heatwaves with both variables exceeding return levels is more obvious. [ABSTRACT FROM AUTHOR]