The net effective temperature (NET), an index that includes the combined effects of temperature, humidity, and wind, was used along with temperature to assess the impacts of climate change on the heat stress perception in East Asia, one of the regions considered most vulnerable to heat stress. The need for dynamic downscaling has been emphasized because the regional effects of climate change do not follow the global levels linearly. In this study, daily maximums calculated from the 3-hourly data downscaled by five different regional climate models from four coupled general circulation models participating in Coordinated Regional Climate Downscaling Experiment-East Asia phase 2 were utilized. To account for the fact human beings acclimate to their environments, 95th percentile of the maximum temperature and maximum NET was used along with the average boreal summer maximum temperatures/NETs. The performance of the models was assessed first, which showed that the models reproduced the current climate well. Future projections revealed an increase in both average and 95th percentile of the maximum temperature and NET over the entire domain for both the RCP8.5 and SSP5-8.5 scenarios. The increase in heat stress (NET) was slightly larger than the temperature itself, with an increase of up to 7/10 C for temperature and 8/11 C for NET in RCP8.5/SSP5-8.5, respectively. The overall increases in temperature and NET were projected to be higher in the higher latitudes, while the increase in the frequency of the temperature and NET extremes was predicted to be higher in the already vulnerable regions in the southern part of the domain.

Numerous extreme climate anomalies were recorded in the northern extratropics in January–March (JFM) 2020, significantly impacting human lives and ecosystems in the affected areas. Those anomalies were caused by an extreme positive Arctic Oscillation (AO) event, with the JFM 2020 AO index of 2.8 being the highest on the record. However, all well-established autumn precursors pointed towards the following wintertime AO phase being negative. Indeed, a negative AO phase was developing until late December when a sudden shift to the strong positive AO event occurred in the troposphere. The geopotential anomalies associated with positive AO spread into the lower stratosphere, and were steadily enhancing throughout JFM resulting in an extreme positive AO event. We show that the strong positive AO event was a result of the destructive interference of the anomalous planetary waves with climatological ones, which led to wave flattening and enhancement of the polar vortex.

<p>Changes in summer heat extremes have been recorded all over the globe in recent years. East Asia is one of the most vulnerable areas for climate change, owing to a combination of natural and anthropogenic factors. The human experience of heat, however, does not only depend on the temperature itself but rather the combination of factors that regulate the exchange of heat with the environment. The present study uses Net Effective Temperature (NET), an index that combines the effects of temperature, humidity, and wind, to assess heat stress perception and its potential changes by the end of the century over East Asia. The data used in the study are maximums calculated from the three-hourly output of the 10 Coupled General Circulation Model (CGCM) - Regional Climate Model (CGM) chains participating in the Coordinated Regional Climate Downscaling Experiment (CORDEX)-East Asia phase 2. As human beings can acclimate to their environment, not only maximum values but also 95th percentiles of maximum values have been used. The assessment of the models showed that all of the models reproduced the current climate reasonably. The present study utilized two different scenarios, RCP8-5, and SSP5-8.5. In both scenarios, the increase in averages and 95th percentiles of both maximum temperatures and NETs over the whole domain has been projected. The increase in NET was projected to be higher than the increase in temperature itself, and the increase in the SSP5-8.5 scenario was projected to be higher than the increase in the RCP8.5 scenario, but the details of the warming patterns were dependent on the choice of model. Additionally, the Korean Peninsula and Japan have been shown to have the largest difference in the increase between heat stress and temperature, while the highest overall increase of both temperature and NET was projected over the North-Western part of the domain in both scenarios.</p>

<p>East Asian Winter Monsoon (EAWM) is an important system, which has impact on extreme winter phenomena, in East Asia including the Korean Peninsula. EAWM is characterized by the Siberian high with cold air and the Aleutian low with warm air, low-level northerly wind between them, East Asian trough in the middle troposphere, and East Asian jet stream in the upper troposphere. According to some previous studies, the variability of EAWM, which can be influenced by human activity and climate change, is strongly correlated with the occurrence of cold waves in East Asia. Additionally, EAWM variability has been shown to affect the precipitation during winter on the Korean Peninsula. Extreme boreal winter phenomena such as cold waves and heavy snow related to EAWM can induce disruptions to regular life and socio-economic damage. Regional climate models (RCMs) have added value in the simulations of extreme climate phenomena, but also have internal variability, which can increase uncertainty in future climate projections. Therefore, in this study, to closely understand EAWM and reduce the uncertainty in future climate projection, the performance of two RCMs (SNURCM and WRF) for EAWM simulation was evaluated. The results showed that two RCMs had the ability to capture the interannual variability and climatological spatial pattern of EAWM despite the systematic biases of EAWM in the lower troposphere (e.g., comparatively low correlation and larger temporal-spatial variability than reanalysis). Additionally, two RCMs presented significant cold bias over the Manchuria and wet bias over the Kuroshio Current. In further analysis, their systematic errors were positively correlated with EAWM, which had a larger pressure gradient between the Siberian high and the Aleutian low and colder advection over Manchuria than those of the ERA5. Wet biases over the Kuroshio Current could be related to unreasonable simulation EAWM induced by uncoupled air-sea interaction in RCMs.</p>

The quantitative assessment of the uncertainty components of future climate projections is critical for decision-makers and organizations to establish climate change adaptation and mitigation strategies at regional or local scales. This is the first study in which the changes in the uncertainty components of future temperature and precipitation projections are quantitatively evaluated using multiple regional climate models over East Asia, vulnerable to future climate change. For temperature, internal variability and model uncertainty were the main factors affecting the near-term projections. The scenario uncertainty continued to increase and was estimated to be the dominant factor affecting the uncertainty after the mid-term projections. Although precipitation has the same main uncertainty factors as the temperature in the near-term projections, it significantly differs from temperature because the internal variability notably contributes to the fraction to the total variance, even in the long-term projections. The internal variability of the temperature and precipitation in the near-term projections was predicted to be larger in Korea than that in East Asia. This was confirmed by regional climate models as well as previous studies using global climate models as to the importance of internal variability at smaller regional scales during the near-term projections. This study is of significance because it provides new possibilities with respect to the consideration of climate uncertainties to the establishment of climate change policies in more detail on the regional scale.