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Quantifying Human Impact on the 2018 Summer Longest Heat Wave in South Korea

© 2019 American Meteorological Society For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy. During summer 2018, South Korea experienced the strongest and longest heat wave since 1973 (the beginning of the observations from 45 stations). The July–August (JA) mean daily maximum temperature (Tmax) was on average 2.6°C warmer than 1987–2010 climatology over South Korea, setting its second highest record after 1994 (Figs. 1a,c). A simple analysis based on a long-term CRU TS data suggests that the return time of 2018 Tmax is about 26 years, much shorter than about 386 years in 1912 (Fig. ES1), although a large uncertainty related to data homogeneity and urbanization effect should be noted (Park et al. 2017). Unusually hot weather led to record-breaking temperatures over many stations with temperature > 40°C at some stations for the first time. More importantly, the 2018 heat wave had the longest duration on record with 31.5 hot days (total number of days with daily maximum temperature > 33°C) surpassing the previous record of 29.7 days in 1994, and exerted considerable impacts on society and the economy (reported in the Korea Herald1,2), including 48 heat-related deaths (KCDC 2018). The heat wave also induced crop destruction in North Korea.3 When using a heat wave duration index (HWDx) defined as maximum consecutive hot days during summer, the 2018 record is extremely high at 18.1 days (Figs. 1b,d). There is a strong correlation between JA mean Tmax and HWDx (r = 0.74; Figs. 1c,d), indicating a close relation between mean warming and heat wave duration. This long-lasting heat wave is characterized by a persistent anomalous high pressure system in the upper troposphere over Korea (Fig. 1f), which seems to be partly induced by the strong tropical convection over northwestern India and the South China Sea (Fig. 1e), through the well-known teleconnection mechanism (Fig. 1g; Lee and Lee 2016; Kim et al. 2019; Yeo et al. 2019). This study aims at quantifying human contribution to the 2018 summer longest duration of heat wave in South Korea. The long duration of heat wave is known to be critically important for health (e.g., Anderson and Bell 2011; D’Ippoliti et al. 2010). To address this question for small spatial scale, we utilize high-resolution large-ensemble regional climate model (RCM) (weather@home East Asia; 50 km) and global climate model (GCM) (HadGEM3-A-N216; 60 km at midlatitudes) simulations, each performed with and without anthropogenic forcings (Table ES1). Comparing two models will help assess the confidence of the resulting attribution statement even though both models are from the Hadley model famQUANTIFYING HUMAN IMPACT ON THE 2018 SUMMER LONGEST HEAT WAVE IN SOUTH KOREA