Executive Summary

In the 6th phase of the Asia-Pacific project (2022-2024), we will advance and improve information of climate monitoring and analysis as well as develop optimizing technology to produce the best forecasts using various information in order to contribute to long-term forecasting and to preemptively respond to extreme climate events. To this end, in the first year, an analysis of the atmospheric variability mechanism in the Atlantic and Indian Oceans and the impact on the Korean Peninsula was performed, taking into account the importance in the recent decades. In order to improve climate prediction information and prepare a basis for optimal utilization of prediction information, qualitative integrated predictions of various predictors were produced and the results were verified. In addition, considering impacts of climate change, the future risk of flooding in the Korean Peninsula and changes in typhoon characteristics were predicted. Finally, the analysis and monitoring system was improved and advanced to perform climate monitoring, analysis and forecasting tasks more efficiently.

Considering the importance in the recent decades, the effects of North Atlantic variability and South Asian High variability on the climates of the Korean Peninsula were examined. The impact of North Atlantic Oscillation (NAO) on the Korean peninsula in spring is nonlinear; When the NAO is in a positive phase, high and low temperatures appear in the Korean Peninsula depending on the difference in tropical SST. In the case of high temperatures on the Korean Peninsula, El Niño in the central Pacific appears and the Indian Ocean is warm, while in the case of low temperatures, La Niña appears in the eastern Pacific and the Indian Ocean is cold. When the NAO is in negative phase, the opposite tendency appears in the Arctic region. When there is above-normal Barents sea ice, there is a below-normal temperatures on the Korean Peninsula, and when there is below-normal sea ice, there is a tendency to show a above-normal temperature.

In the expansion mode during summer, which is the first variability mode of the South Asian High, high sea surface temperatures (SSTs) appear in the Indian Ocean in spring, the temperature rises from the lower atmosphere, and as convection becomes active in the Arabian Sea inJuly, the expansion mode develops further in the upper layer. It was similar to the Indian Ocean capacitance effect that occurs when El Niño in previous winters declines and La Niña develops. In particular, when a positive Pacific North America (PNA) teleconnection appears in July, a anti-cyclonic circulation in the southern part of the Korean Peninsula and a cyclonic circulation in the Korean Peninsula develop, causing below-normal temperature and above-normal precipitation in Korea during July. When the north-south mode, the second variability mode of the South Asian High, moves northward, the Philippine Sea heats up in the spring and convection becomes active in the subtropical Indian Ocean and the western Pacific in summer as weak La Niña continues from the previous winter. It was found that high pressure developed in mid-latitudes due to wave propagation in the south-to-north direction. At the same time, atmospheric waves in the west-to-east direction develop from the warm mid-latitudes of the North Atlantic inducing high pressure on the Korean Peninsula, and the South Asian High moves north. At this time, due to the overlap of high pressure by the wave propagation of the south-to-north direction and the west-to-east direction wave, a strong positive pressure high is developed on the Korean peninsula, resulting in above-normal temperatures in Korea.

In order to prepare the basis for integrating various predictor information, qualitative integration was performed through prior discussions with experts. As a result of the prediction verification, when the temperature in 2022 was neutral or low temperature (March and October), the predictability was better than that of the simple integration. In addition, it was found that the Korean peninsula was hot in the spring of 2022 due to positive NAO and the warm Indian Ocean, and that, in summer, there were few predictors that predicted both atmospheric circulations and temperatures in Korea.

For evaluating the future flood risk of 26 watersheds in South Korea, we analyze the change in extreme precipitation with a 100-year return period under future global warming . In the case of the high CO2 emission scenario, the number of watersheds with a 100-year return period precipitation increase of 50% or more compared to the present climate is predicted to increase significantly in the latter half of the year. On the other hand, in the case of the low-CO2 emission scenario, after the first half of the year, the increase in the extreme precipitation significantly is much less than that of the high-CO2 emission scenario. The above results imply that the possibility of flooding by extreme precipitation can be reduced in the future when the carbon-neutral policy is successfully achieved. In this study, based on the cluster analysis of precipitation events over South Korea, the characteristics of future changes in precipitation-related atmospheric circulation patterns is also analyzed. The first cluster is characterized by the positive 500 geopotential height (GPH) anomaly to the southeast of the Korean Peninsula and a negative 500 GPH anomaly in the northeast, and the second cluster by the positive 500 GPH anomaly in Okhotsk and the negative 500 GPH anomaly around South Korea. The former tends to gradually move northward with future climate change, while the latter shows a characteristic of moving the entire pattern northwards in the middle of the future and moving back around the Korean Peninsula in the latter half.

As a result of analysis of changes in typhoon characteristics on the Korean Peninsula according to future climate change, the Northwest Pacific typhoon activity index decreased at low latitudes, increased at high latitudes, and the change was stronger in the high-CO2 emission scenario during distant-future period. In addition, it is predicted to move further north, expand east and west, and decrease in the equatorial region in the future, which implies that more typhoons will occur in the mid-latitude region closer to the Korean Peninsula. Sea surface temperature also rises steeply, and vertical wind shear, one of the main factors in the occurrence of typhoons, is predicted to weaken in the southern part of the Korean Peninsula. It can affect the Korean Peninsula by acting as a favorable condition for the typhoon to last longer. In addition, using CORDEX-EA, typhoon genesis density, track density, and intensity for 5 regions over the Korean Peninsula and its vicinity are analyzed. Both typhoon genesis and track density are expected to decrease in the Northwest Pacific region and increase in the mid-latitude region close to the Korean Peninsula. Among the 5 regions, the rate of increase in typhoon track density is the largest in regions 3 and 4 in mid-latitudes, where typhoons rarely occurred. In addition, the strength of a typhoon is predicted to become stronger in the high-CO2emission scenario compared to the Historical period. The proportion of typhoons that are stronger than the present increases in all regions, but among them, region 1, region 3, and region 4 show a characteristic of greatly increasing, and the ratio of very strong typhoons compared to the present shows the largest increase in region 3.

Due to the frequently occurring abnormal climate around the world, the need to establish a rapid climate monitoring system is further increasing. In an effort to reduce property and human damage through continuous monitoring of extreme weather conditions that are getting stronger around the world, it is necessary to collect the latest observation data and establish a periodic abnormal weather monitoring system. For quick analysis, climate monitoring service and climate analysis service were developed based on observational data provided by NCEP (National Centers for Environmental Prediction) and KMA (Korea Meteorological Administration). The climate monitoring service provides up-to-date information on various climate variables, and the climate analysis service not only composite of data or provides time-series analysis results, but also standardizes the data collection system to respond quickly to abnormal weather. In addition, an automatic predictor production and information provision system was additionally established for the convenience of users to provide rapid monitoring results. In addition, by establishing a dual system for the convenience of users' research and providing simultaneous service on the internal and external networks in APEC Climate Center, users can freely use the climate analysis system from anywhere. Researchers who mainly use the internal network can directly access and use the climate analysis system on the internal network, thereby increasing work efficiency.