The present study aims to analyze climate change and trend of extreme temperature events occurred over the Republic of Korea. The observation data used are daily average, maximum, and minimum temperature from 6 weather stations for the period of 1912-2020. Seven extreme indices regarding frequency and extreme value of temperature are calculated in seasonal and annual time range. In addition, hot extremes and their changes by four physical terms that include information on the annual mean temperature, the amplitude of the annual cycle, the diurnal temperature range and the local temperature anomaly on the day of the extreme are analyzed. The climatology for the analysis is updated to the new normal year of 1991-2020. Consistent with the previous findings, statistically significant change was detected in the indices of annual lowest daily minimum temperature, annual extreme temperature range, frequency of daily minimum temperature below -12℃ and 10%ile(TN10p) during winter. Due to the gradual decrease of the occurrence days regarding the extreme minimum temperature during winter, the frequency calculated by the relative threshold in extreme high temperature during summer prevail since 1990s. Indices related with extreme high temperature had larger low-frequency variability than significant climate change during the analysis period. However, the assessment of hot extremes according to the terms describing mean, variability and tails during the new normal year of 1991-2020, significant increasing trend was detected not only in the annual mean and the amplitude of the seasonal cycle, but also in the daily hot extreme anomaly.

The purpose of this study is to examine the trends of extreme temperature events in East Asia over the past 40 years (1979-2018) and their potential relationships with recent changes in the Northern Hemisphere cryosphere. Analyses of Sen’s slope and Mann-Kendall tests are performed for time series data of extreme temperature events extracted from NCEP-DOE reanalysis II Gaussian grid daily 2-m air temperature data. As the result, it is found that extreme high temperature events exceeding the 99th percentile show more noticeable increasing trends than the magnitude of the decreasing extreme low temperature events below the 1st percentile particularly in Mongolia, Korean Peninsula and southern China due to unexpected cold events since the late 2000s. Correlation analyses based on Kendall’s tau indicate that the reduction of spring-early summer Eurasian snow cover (data from Rutgers University Global Snow Lab.) may lead to the increasing tendency of extreme high temperature events in East Asia through snow albedo feedbacks, while paradoxically the reducing autumn-early winter Arctic sea ice (data from NSIDC) due to global warming seems to cause more frequent extreme low temperature events in recent years through the amplification of Rossby waves. Thus, it is needed to continue monitoring the feedbacks between changing Arctic cryosphere and East Asian climate systems in the warmer 21st century.

We estimated changes in temperature-related extreme events over South Korea for the mid and late 21st Century using the 122 years (1979-2100) data simulated by RegCM4 with HadGEM2-AO data as boundary conditions. We analyzed the four extreme events (Hot day: HD, Tropical day: TD, Frost day: FD, Icing Day: ID) and five extreme values (Maximum temperature 95/5 percentile: TX95P/TX5P, Minimum temperature 95/5 percentile: TN95P/TN5P, Daily temperature range 95 percentile: DTR95P) based on the absolute and relative thresholds, respectively. Under the global warming conditions, hot extreme indices (HD, TD, TX95P, TN95P) increase, suggesting more frequent and severe extreme events, while cold extreme indices (FD, ID, TX5P, TN5P) decrease their frequency and intensities. In the late 21st Century, changes in extremes are greater in severe global warming scenario, RCP8.5 rather than RCP4.5. HD and TD (FD and ID) are expected to increase (decrease) in the mid 21st Century. The average HD is expected to increase by 14 (17) days in RCP4.5 (8.5). All the percentile indices except for DTR95P are expected to increase in both RCP4.5 and RCP8.5. In the late 21st Century, HD and TD are significantly increased in RCP8.5 compared to RCP4.5, but FD and ID are expected to be significantly reduced. HD is expected to increase mainly in the southwestern region, twice (+41 days) in RCP8.5. TD is expected to increase by 17 days in RCP8.5, which is 5 times greater than that in RCP4.5. TX95P, TN95P and TX5P are expected to increase by about 2°C and 4°C in RCP4.5 and RCP8.5, respectively. TN5P is expected to increase significantly by 4°C and 7°C in RCP4.5 and RCP8.5, respectively.

This study aims to analyze the change of onset and end dates of extreme temperature events and examine their relationships with global warming. The data used for this study are daily maximum temperature, daily minimum temperature, and global mean temperature anomaly. Results were similar to the trend of global temperature, showing that the onset date of extreme high temperature is advanced while the end date of extreme high temperature is delayed. Also, the change of onset (end) dates of extreme low temperature were clear, with coming later (earlier). There is more distinct change in extreme low temperature than extreme high temperature. The length between onset date and end date of extreme high (low) temperature is significantly longer (shorter). The onset (end) date of extreme high temperature has a negative (positive) relationship with global mean temperature. The onset (end) date of extreme low temperature has a positive (negative) relationship with global mean temperature. It might be concluded that the change of onset and end date of extreme temperature in South Korea has been affected by global warming.

Persistent Extreme Temperature Events (PETEs) are defined in two steps; first, to define extreme temperature events, the 80th and 20th percentiles of daily maximum and minimum temperature were chosen. Then individual PETE was defined as an event which lasted three or longer consecutive extreme temperature days. In this study, we examined characteristics and changes of PETEs in Republic of Korea (ROK) using 14 weather stations with a relatively long-term period of data, 1954-2016. In ROK, PETEs lasted four-five days on average and occurred two-three times a year. PETEs lasted longer in summer than in winter and in maximum temperature than in minimum temperature. PETEs which lasted greater than seven days account for a greater proportion in summer than in winter. However, intensities of PETEs were greater in winter because of a larger temperature fluctuation. In both summer and winter, durations and intensities of persistent extreme high temperature events increased while those of persistent extreme low temperature events decreased. Changes of PETEs were closely related with both global warming and diverse large-scale climate variabilities such as AO, NAO and Nino 3.4.

Regional climate simulations for the CORDEX East Asia domain were conducted between 1981 and 2100 using five models to project future climate change based on RCP2.6, 4.5, 6.0, and 8.5 scenarios. By using the ensemble mean of five model results, future changes in climate zones and four extreme temperature events of South Korea were investigated according to Köppen-Trewartha’s classification criteria. The four temporal periods of historical (1981-2005), early future (2021-2040), middle future (2041-2070), and late future (2071-2100) were defined to examine future changes. The analysis domain was divided into 230 administrative districts of South Korea. In historical (1981-2005) period, the subtropical zones are only dominant in the southern coastal regions and Jeju island, while those tend to expand in the future periods. Depending on the RCP scenarios, the more radiative forcing results in the larger subtropical zone over South Korea in the future. The expansion of the subtropical zone in metropolitan areas is more evident than that in rural areas. In addition, the enlargement of the subtropical zone in coastal regions is more prominent than that of in inland regions. Particularly, the subtropical climate zone for the late future period of RCP8.5 scenario is significantly dominant in most South Korea. All scenarios show that cold related extreme temperature events are expected to decrease and hot related extreme temperature events to increase in late future. This study can be utilized by administrative districts for the strategic plan of responses to future climate change.

Extreme temperature has direct and indirect effects on Human Health, and usually influences negatively. This study analyzes the correlation between extreme temperature and excess mortality caused by cardiovascular disease in Seoul. Excess mortality correlates with daily maximum temperature, especially daily excess fatality over two standard deviations, has a strong positive correlation. On the other hand, daily minimum temperature is not significantly related with excess death. Recently, significance of the correlation coefficient of high temperature in August decreases because of the heat wave preparation.

The purpose of this study is to characterize long-term (1973~2012) changes in intra-seasonal temperature and extreme low temperature events in winter observed at 61 weather stations in the Republic of Korea and their associations with changes in atmospheric circulation patterns around East Asia. Maps of long-term linear trends clearly show that both temperature means and extreme events in Korea have asymmetrically changed between early winter and late winter. In early winter, changes with statistical significance are less observable, while in late winter reductions in low extreme temperature events as well as increases in temperatures, particularly after mid-1980s, are obviously observed across the study region. Comparisons of tropospheric synoptic climatic fields before and after the mid-1980s demonstrate that in early winter of recent decades, active meridional circulation from the Arctic appeared in western Eurasia and Bering sea, while in late winter, zonal circulation around East Asia associated with positive Arctic Oscillation-like patterns prevailed. These results indicate that asymmetric changes between early and late winter temperatures in Korea are associated with intra-seasonally inconsistent atmospheric circulation patterns around East Asia.