• Journal of the Korean earth science society
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• v.36 no.3
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• pp.199-209
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• 2015

The Atlantic meridional overturning circulation (AMOC), driven by high density water sinking around Greenland serves as a global climate regulator, because it transports heat and materials in the climate system. We analyzed the mechanism of AMOC on a decadal time scale simulated with the HadGEM2-AO model. The lead-lag regression analysis with AMOC index shows that the decadal variability of the thermohaline circulation in the Atlantic Ocean can be considered as a self-sustained variability. This means that the long-term change of AMOC is related to the instability which is originated from the phase difference between the meridional temperature gradient and the ocean circulation. When the overturning circulation becomes stronger, the heat moves northward and decreases the horizontal temperature-dominated density gradients. Subsequently, this leads to weakening of the circulation, which in turn generates the anomalous cooling at high latitudes and, thereby strengthening the AMOC. In this mechanism, the density anomalies at high latitudes are controlled by the thermal advection from low latitudes, meaning that the variation of the AMOC is thermally driven and not salinity driven.

• Journal of Korea Water Resources Association
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• v.45 no.9
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• pp.887-900
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• 2012

Drought is a non-negligible disaster of nature and it is mainly caused by rainfall shortage for a long time though there are many definitions of drought. 'Standard Precipitation Index' (SPI) that is widely used to express the level of meteorological drought intensity has a limit of not being able to consider the hydrological changes such as rainfall and evapotranspiration caused by climate change, because it does not consider the temperature-related variables other than the precipitation. Recently, however, 'Standardized Precipitation Evapotranspiration Index' (SPEI), a drought index of new concept which is similar to SPI but can reflect the effect of temperature variability as well as the rainfall change caused by climate variation, was developed. In this study, the changes of drought occurrence in South Korea were analyzed by applying SPEI for meteorological data (1973~2011) of 60 climate observatories under Korea Meteorological Administration (KMA). As the result of application, both of SPI and SPEI showed the trend of deepening drought in spring and winter and mitigating drought in summer for the entire nation, with SPI showing greater drought intensity than SPI. Also, SPI and SPEI with 12 months of duration showed that severe droughts with low frequency of around 6 years are generally being repeated.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.178-178
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• 2023

Drought and flooding have historically coexisted in Korea, occurring at different times and with varying cycles and trends. The drought indicators measured were (PDSI), (SPI), and (SPEI) in order to statistically analyze the annual or periodic drought occurrence and objectively evaluate statistical characteristics such as the periodicity, tendency, and frequency of occurrence of droughts in the Doam watershed. To compute potential evapotranspiration (PET), both Thornthwaite (Thor) and Penman-Monteith (PM) parameterizations were considered, and the differences between the two PET estimators were analyzed. Hence, SPIs 3 and SPIs 6 revealed a tendency to worsen drought in the spring and winter and a tendency to alleviate drought in the summer in the study area. The seasonal variability trend did not occur in the SPIs 12 and PDSI, as it did in the drought index over a short period. As a result of the drought trend study, the drought from winter to spring gets more severe, in addition to the duration of the drought, although the periodicity of the recurrence of the drought ranged from 3 years to 6 years at the longest, indicating that SPIs 3 showed a brief time of around 1 year. SPIs 6 and SPIs 12 had a term of 4 to 6 years, and PDSI had a period of roughly 6 years. Based on the indicators of the PDSI, SPI, and SPEI, the drought severity increases under climate change conditions with the decrease in precipitation and increased water demand as a consequence of the temperature increase. Therefore, our findings show that national and practical measures are needed for both winter and spring droughts, which happen every year, as well as large-scale and extreme droughts, which happen every six years.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1465-1469
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• 2006

수문순환 과정은 기상현상과 밀접한 관련을 가지고 서로 연관되어 있다. 이러한 연관성을 규명하여 수자원관리에 위험도를 감소시키려는 노력은 많은 분야에서 이루어지고 있으며, 주요 연구 주제가 되고 있다. 이러한 기상현상 중에서 가뭄은 여러 가지 요소가 복합되어 발생되는 것으로 알려지고 있으나 이를 설명하기에는 여전히 부족한 면이 존재한다. 가뭄을 발생시키는 몇 가지 가능한 원인으로는 E1 Nino-Southern Oscillation(ENSO)현상으로 잘 알려져 있는 비정상적인 해수면 온도의 변화나 기후 시스템의 비선형적 거동을 들 수 있다. 특히, 기후 시스템은 대개 경년 변화(inter-annual variability) 및 10년 이상의 주기(decadal variability) 특성을 가지고 있으며 가뭄 또한 경년변화의 주기 특성을 나타내고 있는 것으로 알려지고 있다. 이러한 관점에서 수문시계열을 특정 주파수(frequency)에서 고립시킨 후, 분석이 가능한 분해방법(decomposition method)을 통해 보다 해석적으로 접근하는 것이 가능하다. 이를 위해 본 연구에서는 Wavelet Transform분석을 도입하였으며 통계적으로 유의한 성분을 시계열로부터 추출하여 가뭄과 기상인자와의 변동성 분석을 실시하였다.

• Journal of Wetlands Research
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• v.13 no.1
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• pp.1-11
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• 2011

A chronic drought stress has been imposed during non-rainy season(from winter to spring) since 1990s. We faced the most significant water crisis in 2001, and the drought was characterized by sultry weather and severe drought on a national scale. It has been widely acknowledged that the drought related damage is 2-3 times serious than floods. In the list of the world's largest natural disaster compiled by NOAA, 4 of the top 5 disasters are droughts. And according to the analysis from the NDMC report, the drought has the highest annual average damage among all the disasters. There was a very serious impact on the economic such as rising consumer price during the 2001 spring drought in Korea. There has been flood prevention measures implemented at national-level but for mitigation of droughts, there are only plans aimed at emergency (short-term) restoration rather than the comprehensive preventive measures. In addition, there is a lack of a clear set of indicators to express drought situation objectively, and therefore it is important and urgent to begin a systematic study. In this study, a nonstationary downscaling model using RCM based climate change scenario was first applied to simulate precipitation, and the simulated precipitation data was used to derive Standardized Precipitation Index (SPI). The SPI under climate change was used to evaluate the spatio-temporal variability of drought through principal component analysis at three different time scales which are 2015, 2045 and 2075. It was found that spatio-temporal variability is likely to modulate with climate change.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.5
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• pp.55-65
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• 2014

Radar remote sensing is appropriate for rice monitoring because the areas where this crop is cultivated are often cloudy and rainy. Especially, Synthetic Aperture Radar (SAR) can acquire remote sensing information with a high temporal resolution in tropical and subtropical regions due to its all-weather capability. This paper analyzes the relationships between backscattering coefficients of rice measured by RADARSAT-2 SAR and growth parameters during a rice growth period. And we applied the relationships to crop monitoring of paddy rice in North Korea. As a result, plant height and Leaf Area Index (LAI) increased until Day Of Year (DOY) 234 and then decreased, while fresh weight and dry weight increased until DOY 253. Correlation coefficients revealed that Horizontal transmit and Horizontal receive polarization (HH)-polarization backscattering coefficients were correlated highly with plant height (r=0.95), fresh weight (r=0.92), vegetation water content (r=0.91), LAI (r=0.90), and dry weight (r=0.89). Based on the observed relationships between backscattering coefficients and variables of cultivation, prediction equations were developed using the HH-polarization backscattering coefficients. Concerning the evaluation for the applicability of the LAI distribution from RADARSAT-2, the LAI statistic was evaluated in comparison with LAI distribution from RapidEye image. And LAI distributions in Pyongyang were presented to show spatial variability for unaccessible areas.

• Journal of The Korean Society of Agricultural Engineers
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• v.61 no.3
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• pp.77-88
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• 2019

Drought is the recurrent natural disasters which harshly affect agricultural production and society in various parts in Bangladesh. Information on the spatiotemporal variability of drought events plays a vital role to take necessary action towards drought mitigation and sustainable development. This study aims to analyze the spatial and temporal variation of meteorological drought in Bangladesh during 1981-2015 using Effective Drought Index (EDI). Monthly precipitation data for 36 years (1980-2015) were obtained from 27 meteorological stations. Drought frequency (DF) and areal extent of drought were considered to investigate the spatiotemporal structure of drought. The DF analysis showed that the northern, southwestern and central regions of the country are comparatively vulnerable to meteorological drought. The frequency of drought in all categories has considerably increased during the recent five years from 2011 to 2015. Furthermore, the most significant increasing trend of the drought-affected area was found over the central region especially for pre-monsoon (March-May) season during this period while the decreasing trend of the affected area was found within the eastern region during the study period. To prevent and mitigate the damages of drought disasters in Bangladesh, agricultural and government managers should pay more attention to those regional drought events that occur in pre-monsoon season. The outcome of the present study can be used as explanatory data in building the strategies to drought monitoring and mitigation activities in Bangladesh.

• Journal of People, Plants, and Environment
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• v.22 no.3
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• pp.309-319
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• 2019

This study was conducted to investigate the effects of watching a virtual reality (VR) forest video on stress reduction in adults. Experiments were performed in an artificial climate chamber where temperature, humidity and illumination were controlled. To cause stress in subjects, the subjects were asked to multiply two digit numbers by one digit numbers for two minutes. The subjects then watched a VR forest video for five minutes. During the experiment, the heart rate variability (HRV) and heart rate (HR) of subjects were continuously measured for evaluating their physiological state. After measuring the baseline and watching a VR forest video, their psychological state was evaluated using the profile of mood state (POMS), semantic differential (SD) method, and positive affect and negative affect schedule (PANAS). The results of physiological evaluation after watching a VR forest video showed a decrease in the stress index and HR, an increase in the activity of the parasympathetic nervous system, and the standard deviation of normal to normal RR intervals (SDNN). The results of psychological assessment confirmed that watching a VR forest video induced "comfort", "natural", and "soothed" feelings in subjects. In addition, watching a VR forest video decreased "tension-anxiety (T-A)", "depression-dejection (D)", "anger-hostility (A-H)", "fatigue (F)", "total mood disturbance (TMD)", and increased "vigor (V)" compared to the base line, and decreased "negative affect" and increased "positive affect." These results indicate that watching a VR forest video decreases adults' stress index, stabilizes physiological state, and has a positive impact on psychological state. The findings of this study can serve as a basis for providing forest welfare services to people in the blind spots of forest welfare, and can lay a foundation for the adoption of VR, one of the technologies of the fourth industrial revolution in forestry.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.309-319
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• 2015

River characteristics in South Korea has been affected by seasonal climatic variability due to climate change and by remarkable land cover change due to rapid economic growth. In this regard, the roles of river management is getting more important to eco-system and human community in watersheds of South Korea. Understanding river characteristics including direct runoff and baseflow, the first step of river management, can give a significant contribution to sustainable river environment. Therefore, the objective of this study is to quantify the contributions of the direct runoff and baseflow to river streamflow. For this, we used the BFLOW and WHAT programs to conduct baseflow separation for 71 streamflow gauge stations in Han River system, South Korea. The results showed that baseflow index for 71 stations ranges from 0.42 to 0.78. Also, gauge stations which have baseflow index more than 0.5 occupied 76% of a total stations. However, baseflow index can be overestimated due to human impacts such as discharge from dams, reservoirs, and lakes. This study will be used as fundamental information to understand river characteristics in river management at the national level.

• Journal of Wetlands Research
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• v.13 no.3
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• pp.499-514
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• 2011

An underlying assumption of traditional hydrologic frequency analysis is that climate, and hence the frequency of hydrologic events, is stationary, or unchanging over time. Under stationary conditions, the distribution of the variable of interest is invariant to temporal translation. Water resources infrastructure planning and design, such as dams, levees, canals, bridges, and culverts, relies on an understanding of past conditions and projection of future conditions. But, Water managers have always known our world is inherently non-stationary, and they routinely deal with this in management and planning. The aim of this paper is to give a brief introduction to non-stationary extreme value analysis methods. In this paper, a non-stationary hydrologic frequency analysis approach is introduced in order to determine probability rainfall consider changing climate. The non-stationary statistical approach is based on the conditional Generalized Extreme Value(GEV) distribution and Maximum Likelihood parameter estimation. This method are applied to the annual maximum 24 hours-rainfall. The results show that the non-stationary GEV approach is suitable for determining probability rainfall for changing climate, sucha sa trend, Moreover, Non-stationary frequency analyzed using SOI(Southern Oscillation Index) of ENSO(El Nino Southern Oscillation).