Spatiotemporal extension of extreme heat stress over East Asia under shared socioeconomic pathways

This study examines future changes in extreme heat stress over East Asia and its sub-regions using wet bulb globe temperature (WBGT) based on the CORDEX East Asia Phase II multiple Regional Climate Model (RCM) simulations performed under Shared Socioeconomic Pathways (SSP) scenarios. Daily maximum WBGTs (WX) are obtained from 3-hourly bias-corrected WBGTs and their future changes in the late 21st century (2081-2100) are analyzed with respect to the current period (1979-2014). Summer mean WX is projected to increase by 3.2 degrees C (SSP1-2.6: low emission) to 7.6 degrees C (SSP5-8.5: high emission) over East Asia, dominated by temperature increases. Relative humidity decreases over many regions, slightly offsetting WX increases (up to-6%), while it increases in northeastern and northern China, intensifying WX increases (up to +14%). This humidity-induced WX increase becomes stronger during hottest WX days (summer top 5%) and also under low emission scenarios (up to +33%). For sub-regional projections, extreme heat stress day (EHD) is defined when WX exceeds its 95th percentile in at least 10% of the area. RCMs project on average a 10 times increase of EHD frequency under the SSP5-8.5 scenario. The EHD magnitude, which combines the intensity and area extent of EHD events, is also expected to increase dramatically throughout East Asia, reaching a range of 3.2-3.5 degrees C center dot fraction compared to the current (0.1-0.2 degrees C center dot fraction). Further, EHDs are projected to start earlier and end later, lasting much longer (85-140 days) than the current condition (5-6 days) in the SSP5-8.5 scenario. RCMs exhibit a good agreement in WX and EHD projections with some noticeable differences in in-land sub-regions. Our results indicate that severe heat stress will affect the whole East Asia throughout and beyond the summer season and, in particular, southern sub-regions will be affected by more-intense and longer-lasting extreme heat stress events.