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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 considerably 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 were 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 meaningful 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. [ABSTRACT FROM AUTHOR]

To explore sea level transgression in low-lying inland areas and its possible influence on prehistoric cultures, we investigated the physical and geochemical features of 20-m-long sedimentary cores from the previously seawater-filled Daesan Basin located in the middle reach of the present Nakdong River in Korea as proxies for seawater transgression deep inland areas due to Holocene sea level rise. Based on the relationships among grain size, total sulfur content (TS%), and carbon/sulfur (C/S) ratio, the first transgressive event was detected at ca. 8500 cal yr BP, caused by seawater influx along the present Nakdong River. Higher TS% (0.8-1%) and interbedded fossil oysters at 8000-6000 cal yr BP indicate marine environments, supporting a paleo-Daesan Bay with water depth of ~10-8m. The common peaks in TS%, in both inland paleo-Daesan Bay and a present coastal area (Suncheon Bay) in southern Korea (e.g., at 3200 and 4700 cal yr BP), may indicate intervals of higher salinity, which suggests simultaneous responses to changes in sea level or hydroclimate. The duration of marine environment (paleo-Daesan Bay) in the remote inland from ca. 8000-3200 cal yr BP provides an analog for inland paleo-bay studies in East Asia. [ABSTRACT FROM AUTHOR]

Understanding the spatiotemporal variability of extreme hydrologic events, especially those driven by typhoons over Asia, and their controlling factors is essential to testing and predicting their future changes under global warming. Here, we present a series of direct heavy-rainfall records over the past ca. 10,000 years based on lake sediments from a volcanic cone (Sara Oreum) on Jeju Island, Korea, where orographic amplification of precipitation is dominant and sensitive to present typhoon activity. The reconstructed heavy rainfall index based on the high-resolution elemental ratios (e.g., Ti/Al and Sr/Si) shows clear variability at centennial timescales and is similar to records of coastal flooding events along the southern coast of Korea, typhoon-driven overwash events along the south-western coast of Japan, indicating strong typhoon influence on the heavy rainfall events in Jeju Island during the Holocene. Furthermore, this heavy rainfall-typhoon linkage has been influenced by past El Niño–Southern Oscillation (ENSO) activity and sea surface temperature (SST) in the western Tropical Pacific, showing time-varying influences. This study suggests that on decadal to multi-centennial timescales, stronger ENSO activity is responsible for eastward shift in the location of typhoon genesis, resulting in more frequent recurving tracks of typhoon and increased landfalls in Korea and Japan, whereas SST affects the intensification rate of typhoon. The heavy rainfall index reconstructed from the volcanic cones of Jeju Island may be used as an indicator of past frequency and track changes of typhoon over highly populated East Asia. • The heavy rainfall index (e.g., Ti/Al and Sr/Si) shows clear variability at decadal-to-centennial timescales. • This heavy rainfall-typhoon linkage has been influenced by ENSO activity and sea surface temperature. • The heavy rainfall index can be used as an indicator of past frequency and track changes of typhoon. [ABSTRACT FROM AUTHOR]

In East Asia, freshwater inputs in coastal areas are mainly controlled by rainfall occurring during the East Asian summer monsoon (EASM), which is linked to seasonal latitudinal shifts in the intertropical convergence zone (ITCZ). To investigate the centennial-time-scale relationship between those inputs and the seasonal shifts in the ITCZ, we examined the behaviors of terrestrial input proxies in coastal sediments of western Korea, including grain size, elemental ratios from XRF core scanning (e.g., Zr/Ti and Si/Al), and C/N ratios. Correlation tests linked these proxies to past freshwater input variability, suggesting that elemental ratios can serve as a proxy for past EASM changes. During the period 8500–7800 cal yr BP, the stronger EASMs described by high-resolution peaks of Zr/Ti ratios corresponded to periods of intensified Indian summer monsoons (ISMs) and weakened South American summer monsoon (SASMs), supporting the existence of synchronous global monsoon (GM) events induced by a northward ITCZ shift. This study also shows that the 8.2-ka cooling event recorded in Greenland ice cores synchronously influenced the GM through a southward shift in the ITCZ, resulting in a weakened EASM and ISM in the Northern Hemisphere and an intensified SASM in the Southern Hemisphere. Our study thus demonstrates that the elemental ratios in coastal sediments measured using an XRF core scanner can be utilized to trace high-resolution (at least centennial-time-scale) variability in the EASM in terms of GM-ITCZ coupling. • Zr/Ti and Si/Al ratios from XRF core scanning and C/N ratios were tested to reconstruct past freshwater input. • Strong EASMs described by peaks of Zr/Ti ratios corresponded to intensified ISMs and weakened SASMs. • Elemental ratios from XRF core scanning can be utilized to trace EASM in terms of GM-ITCZ coupling. [ABSTRACT FROM AUTHOR]