Future changes in extreme heatwaves in terms of intensity and duration over the CORDEX-East Asia Phase Two domain using multi-GCM and multi-RCM chains

Abstract

An extreme heatwave, in terms of intensity and duration, is projected to occur at the end of the 21st century (2071-2100) over the whole of East Asia. The projection is calculated using daily maximum temperature data of 25 km horizontal resolution produced by 12 general circulation model-regional climate model chains participating in the CORDEX-East Asia Phase 2 project. An 'extreme' heatwave is defined as one in which the heatwave magnitude (HWM), which is the accumulated daily intensity of a heatwave during the heatwave period, is higher than the 95th percentile of the HWM for the reference period (1981-2005). In historical simulations, heatwaves have occurred mainly from April to June in India, in April and May in Indochina, from June to August in China and Mongolia, and in July and August in the Korean Peninsula and Japan; most heatwaves last three to four days. In India and Indochina, long-lasting and intense heatwaves occur more often than in other regions. In future, heatwave intensity will increase, the average duration of heatwaves will be approximately two to three weeks, and the heatwave season will be lengthened. Therefore, extreme heatwaves will occur more frequently and strongly. Under two representative concentration pathway scenarios (RCP2.6 and RCP8.5) and two shared socioeconomic pathway scenarios (SSP1-2.6 and SSP5-8.5), the proportion of extreme heatwaves to all heatwave events will increase from 5.0% (historical) to 8.0%, 20.8%, 19.3%, and 36.3%, and the HWM of the extreme heatwave will be 1.4, 3.5, 3.0, and 9.0 times stronger, respectively. The main reason for the increase in the HWM of extreme heatwaves is the increased duration rather than the daily intensity of the heatwaves. In East Asia, the temporal and regional disparities of heatwave damage will be much more prominent as extreme heatwaves become stronger and more frequent in these regions and during the periods that are more affected by heatwaves in the present day.