Although climate change-related concerns have long been raised regarding the sudden dieback of Korean fir (Abies koreana), the event's etiology and subsequent ecosystem processes must be explained. Our study aims to clarify the continuity or transience of mass mortality events within the coarse woody debris (CWD) structure and, if transient, to identify the climatic conditions (1974-2021) that could be responsible for the massive dying phenomena in Korean fir populations. On average, precipitation during the non-growing season (November-April as winter) constituted 18.5% relative to the growth period; in the winter of 1999, it was 4.8% due to an abnormal drought event. The dead stems occurred evenly across all size classes. In the CWD structure, the density and biomass of the dead fir individuals peaked in decay classes II or III. The size distribution of the retained fir was inverse-J shaped across the entire altitudinal range. The abnormal winter drought event, causing root damage by soil frost and heaving, may be one of the factors that increased Korean fir mortality across the entire stem size range. Despite transient cohort senescence, the retained Korean fir individuals transmitted drought-resistant traits into the regional pool following the drought event.
Recently, global urbanization and industrialization have resulted in excessive groundwater exploitation, and the occurrence and damage of land subsidence to human life and property are increasing accordingly. The present study assessed the impact of tunnel excavation on the groundwater system and potential land subsidence in a Korean metropolitan area. A numerical model was established to predict groundwater level variations with tunnel excavation, and the mechanisms and cases of land subsidence worldwide were reviewed. The established model adequately represented the groundwater system in the study area. The tunnel excavation decreased the groundwater level along the tunnel line, and significant groundwater drawdown primarily occurred up to 6.1 m at locations with high permeability, leading to the temporary development of a large depression cone. The study area has favorable conditions for land subsidence, and curved tunnel excavation may induce ground disturbance, resulting in groundwater inflow and soil loss in the region. In addition, the risk of land subsidence is expected to persist owing to the lag time caused by the creep phenomenon, even though the groundwater level recovers. Efforts to effectively reduce land subsidence damage in urban areas are crucial, requiring measures such as controlling land subsidence occurrence and implementing prevention measures through early recognition, including artificial recharge of groundwater, underground cavity observation with ground penetrating radar, land subsidence observation with a borehole extensometer, and groundwater level monitoring systems.
East Asia is the strongest global source region for anthropogenic black carbon (BC), the most important light-absorbing aerosol contributing to direct radiative climate forcing. To provide extended observational constraints on regional BC distributions and impacts, in situ measurements of BC were obtained with a single particle soot photometer during the May/June 2016 Korean-United States Air Quality aircraft campaign (KORUS-AQ) in South Korea. Unique chemical tracer relationships were associated with BC sourced from different regions. The extent and variability in vertical BC mass burden for 48 profiles over a single site near Seoul were investigated using back trajectory and chemical tracer analysis. Meteorologically driven changes in transport influenced the relative importance of different source regions, impacting observed BC loadings at all altitudes. Internal mixing and size distributions of BC further demonstrated dependence on source region: BC attributed to China had a larger mass median diameter (18013nm) than BC attributed to South Korea (15225nm), and BC associated with long-range transport was less thickly coated (604nm) than that sourced from South Korea (7516nm). The column BC direct radiative effect at the top of the atmosphere was estimated to be 1.0-0.5+0.9W/m(2), with average values for different meteorological periods varying by a factor of 2 due to changes in the BC vertical profile. During the campaign, BC sourced from South Korea ( 31%), China (22%), and Russia (14%) were the most significant single-region contributors to the column direct radiative effect.
Regional air quality modelling was used to simulate the distribution of BC aerosol over the Korean Peninsula for four mid-season months of 2009. Compared to ground-based and satellite observations, the model underestimated the average BC burden significantly, which might be attributed to inaccuracy in BC emissions inventories partly due to the neglect of the emissions from biomass burning although it is not possible to rule out inaccurate prediction of meteorology. The model-estimated monthly average BC burden was highest in winter because of the largest emission. When the BC burden was divided by the monthly emission factor, the adjusted BC burden was much higher in spring and fall than in winter and summer due to strong influence of Chinese source conveyed by westerly wind prevailing in spring and fall. Both long-range transport and local sources were shown to contribute to atmospheric BC over the Korean Peninsula. Urban areas were influenced more by local sources while the effect of long-range transport was higher in remote areas. Based on the model simulations, the direct radiative forcing (DRF) of BC was estimated to be 0.1-1.8 W m(-2) over the Korean Peninsula with the domain-average value of 0.39 W m(-2). Accounting for the model underestimation of absorbing aerosol optical depth by BC by 48% compared to measured monthly averages due to the underestimated emissions inventories, the adjusted average DRF is 0.75 W m(-2). 2012 Elsevier Ltd. All rights reserved.