Journal of the Korean Society of Hazard Mitigation
The current heatwave crisis alert system considers the daily maximum temperature alone; therefore... more The current heatwave crisis alert system considers the daily maximum temperature alone; therefore, the present study proposed a new method for estimating the daily heatwave crisis alert level. Specifically, the heatwave risk index was calculated by combining regional vulnerability, as estimated using principal component analysis, and normalized daily maximum temperature. The crisis alert level was classified according to the risk index value using the natural breaks method. The correlation coefficient between the heatwave risk index and heat-related morbidity rate was approximately 0.4. In addition, analysis of variance confirmed significant differences in the heat-related morbidity rate among different crisis alert levels. The current method is limited in that it does not take into account the various regional environmental characteristics, which may results in an ambiguous alert standard; however, this shortcoming may be resolved using the proposed heatwave risk index. Therefore, ...
KSCE Journal of Civil and Environmental Engineering Research, Dec 1, 2018
It is necessary to determine an optimal design frequency for establishing stable flood control ag... more It is necessary to determine an optimal design frequency for establishing stable flood control against frequent flood disasters. Depending on the importance of river and regional characteristics, design return periods are suggested from at least 50 years up to 200 years for river design. However, due to the wide range of applications, it is not desirable to reflect the geographical and flood control characteristics of river. In this study, Bayes theory was applied to seven evaluation factors to determine the optimal design return period of rivers in Chungcheongnam-do; urbanization flooded area, watershed area, basin coefficient, slope, water system and stream order, range of backwater effect, abnormal rainfall occurrence frequency. The potential flood damage (PFD) capacity was estimated considering climate change and the appropriate design return period was determined by analyzing the capacity of each district. We compared the design return periods of 382 rivers in Chungcheongnam-do with the existing design return periods. The number of rivers that were upgraded from the existing return period were 65, which have relatively large flooding areas and have large PFDs. Whereas, the number of rivers that were downgraded were 169.
Considering the effect of climate change, a quantitative analysis of extreme drought is needed to... more Considering the effect of climate change, a quantitative analysis of extreme drought is needed to reduce the damage from extreme droughts. Therefore, in this study, a quantitative risk analysis of extreme drought was conducted. The threshold level method was applied to define a drought event using Cheugugi rainfall data in past, gauged rainfall data in present, and climate change scenario rainfall data in future. A bivariate drought frequency analysis was performed using the copula function to simultaneously consider two major drought characteristics such as duration and severity. Based on the bivariate drought frequency curves, the risks for the past, present and future were calculated and the risks for future extreme drought were analyzed comparing with the past and present. As a result, the mean drought duration of the future was shorter than that of past and present, however, the mean drought severity was much larger. Therefore short term and severe droughts were expected to occur in the future. In addition, the analysis of the maximum drought risk indicated that the future maximum drought risk was 1.39~1.94 times and 1.33~1.81 times higher than the past and present. Finally, the risk of extreme drought over past and present maximum drought in the future was very high, ranging from 0.989 to 1.0, and the occurrence probability of extreme drought was high in the future.
Soil moisture is a crucial factor in hydrological system which influences runoff, energy balance,... more Soil moisture is a crucial factor in hydrological system which influences runoff, energy balance, evaporation, and atmosphere. United States National Aeronautic and Space Administration (NASA) and Department of Agriculture (USDA) have established Soil Moisture Experiment (SMEX) since 2002 for the global observations. SMEX provides useful data for the hydrological science including soil moisture and hydrometeorological variables. The purpose of this study is to investigate the relationship between remotely sensed soil moisture data from aircraft and satellite and ground based experiment. C-band of Polarimetric Scanning Radiometer (PSR) that observed the brightness temperature provides soil moisture data using a retrieval algorithm. It was compared with the In-situ data for 2-30 cm depth at four sites. The most significant depth is 2-10 cm from the correlation analysis. Most of the sites, two data are similar to the mean of data at 10 cm and the median at 7 cm and 10 cm at the 10% sig...
Rapid eye movement (REM) sleep without atonia (RSWA) fulfils one of the criteria for diagnosing R... more Rapid eye movement (REM) sleep without atonia (RSWA) fulfils one of the criteria for diagnosing REM sleep behavior disorder (RBD) according to the International Classification of Sleep Disorders, Third Edition. However, RSWA quantification is an unresolved issue, which is associated with the future direction of revising the diagnostic criteria. The purpose of this study was to evaluate the quantification of RSWA in patients with RBD and identify an optimal cutoff value of quantitative RSWA for RBD diagnosis. Methods: Medical records and polysomnographic results were analyzed retrospectively to diagnose sleep disorders from June 2017 to May 2018 at Pusan National University Hospital. Nineteen subjects with idiopathic RBD were included in the present study. Propensity score matching was used to control age, gender, and anti-depressant factors, which influenced RSWA. RSWA was scored according to the American Academy of Sleep Medicine scoring manual. Cohen's kappa coefficient was measured to test inter-rater reliability between two polysomnography raters. Results: Cohen's kappa coefficients were 0.755 (p<0.001) and 0.689 (p<0.001) for tonic and phasic activities, respectively. RSWA was significantly increased in subjects with RBD compared with controls [median and interquartile range: 16.5 (8.8-24.6) vs. 6.3 (4.1-7.2) p=0.001]. The optimal cutoff value was 8.0% for the proportion of RSWA (sensitivity 78.5%, specificity 85.7%, area under the receiver-operating characteristic curve 0.837). Conclusions: Subjects with RBD had significantly increased RSWA compared to controls. The proportion of RSWA during REM sleep can be applied to discriminate subjects with RBD from controls.
Journal of korean society of hazard mitigation, 2013
This paper sets forth key concepts and advances working definitions for sustainable and resilient... more This paper sets forth key concepts and advances working definitions for sustainable and resilient infrastructures (S&R-Infra), specifically for water systems. Three water infrastructure scales, such as large, medium, and small scales are considered, each of which is represented by water resource system, regional water and wastewater infrastructure, and local water distribution system, respectively. All three scales are interconnected each other since water travels from sources to end users and returns the other way. This study is beneficial by suggesting indicators to evaluate system sustainability and resilience against outer disturbances. After S&R definitions and potential indicators are provided, application examples are examined to demonstrate the applications of the proposed indicators. Application results show that the proposed indices are useful for quantifying water system performance. While the approach is refined and applied to synthetic cases, it may be considered applicable to real-world systems as system performance indicators and/or system planning and design goals within an optimization framework.
Due to the increased water demand and severe drought as an effect of the global warming, the effl... more Due to the increased water demand and severe drought as an effect of the global warming, the effluent from wastewater treatment plants becomes considered as an alternative water source to supply agricultural, industrial, and public (gardening) water demand. The effluent from the wastewater treatment plant is a sustainable water source because of its good quality and stable amount of water discharge. In this study, the water reuse system was developed to minimize total construction cost to cope with the uncertain water demand in future using two-stage stochastic linear programming with binary variables. The pipes in the water reuse network were constructed in two stages of which in the first stage, the water demands of users are assumed to be known, while the water demands in the second stage have uncertainty in the predicted value. However, the water reuse system has to be designed now when the future water demands are not known precisely. Therefore, the construction of a pipe parallel with the existing one was allowed to meet the increased water demands in the second stage. As a result, the trade-off of construction costs between a pipe with large diameter and two pipes having small diameters was evaluated and the optimal solution was found. Three scenarios for the future water demand were selected and a hypothetical water reuse network considering the uncertainties was optimized. The results provide the information about the economies of scale in the water reuse network and the long range water supply plan.
Journal of korean society of hazard mitigation, 2013
In Korea, the occurrence frequency of earthquakes has recently increased compared to the past. In... more In Korea, the occurrence frequency of earthquakes has recently increased compared to the past. In neighboring countries such as Japan and China, damage from major earthquakes has also increased leading to high earthquake risk. This study quantitatively estimated the occurrence probability and frequency of huge earthquake using statistical frequency analysis on instrumental earthquake data at East sea in order to cope with earthquake damage. After adapting Various distribution functions such as Gumbel, Lognormal, Gamma, and Weibull for earthquake data, we applied mixed distributions to reflect the characteristics of the occurrence of earthquakes. The results show that the mixed models estimated earthquake magnitude larger than the Gutenberg-Richter (G-R) equation, and the mixed Gumbel distribution estimated most closed values with the G-R equation. It was found that the G-R equation is very limited to estimate a huge earthquake since there is no observed data over magnitude 8.0 and the frequency analysis is also limited to be applied in practice because the lack of data induces high uncertainty on the estimates of 1,000 year-earthquake. However, this study has an experiential significance in that the statistical frequency analysis was applied to instrumental earthquake data at East sea as an alternative.
Journal of korean society of hazard mitigation, 2012
This study proposed a practical approach to estimate design rainfalls that can be applied to desi... more This study proposed a practical approach to estimate design rainfalls that can be applied to design reference year using the relationships among distribution parameters, annual rainfalls estimated from GCMs(Global Circulation Models), and annual maximum rainfalls observed at gauging stations, leading to consider climate change. The highlight of this study is to estimate distribution parameters through regression models with annual rainfalls as a causal factor. The proposed model was applied to estimated ensemble design rainfalls with 24-hr duration in built-up design reference years of 2020 and 2030 at 10 stations considering the uncertainty induced by emission scenarios and GCMs. The overall results indicated that the design rainfalls of Gangneung, Daejeon, Seoul, and Sokcho in 2020 and 2030 are higher than those in 2009(assumed as the current), the design rainfalls of Gwangju, Seosan, and Jeju in 2020 and 2030 are very close to the current, and the design rainfalls of Busan, Mokpo, and Daegu in 2020 and 2030 are lower than the current. It is considered that the trend component of the annual maximum rainfalls is incorporated into the process of estimating design rainfalls. The proposed method can provide design rainfalls in the next 10 more years in which the effect of climate change is reflected, and thus may suggest useful reference or alternatives for the hydrologic plan and management.
Accurate prediction of reservoir sediment inflows (Min) and adaptation of feasible sediment manag... more Accurate prediction of reservoir sediment inflows (Min) and adaptation of feasible sediment management strategies pose challenges in water engineering. This study proposed a two-stage complementary modeling approach for comprehensive reservoir sediment management. In the first stage, artificial neural network-based models provide real-time Min predictions using water inflow, water head, and outflow as input parameters. In the second stage, the parameter estimation method of the RESCON model is applied to hydraulic flushing in a reservoir. This approach was applied to the Sangju Weir and Nakdong River Estuary Barrage (NREB) in South Korea. Results from the RESCON model revealed that hydraulic flushing was effective for sediment management at both the Sangju Weir reservoir and the NREB approach channel. Efficient flushing at the Sangju Weir required a flushing discharge of 100 m3/s for 6 days and 40 m of water head. Efficient flushing at the NREB required a flushing discharge of 25 m3/s for 6 days with 1.8 m of water-level drawdown. The proposed approach is expected to prove useful in reservoir sediment management.
The soil-water interaction is crucial for effective hydrological processes determination. The soi... more The soil-water interaction is crucial for effective hydrological processes determination. The soil moisture (SM) is an important parameter to provide priori information for the interactions imparting and affecting the energy fluxes response for such kind of processes. This work investigated the effects of climatic, geophysical and hydrological parameters on SM at 9 stations within Utah State, USA, for daily data recorded between 2010 and 2012 at 5 different soil depths (approximately 5, 10, 20, 50, and 100 cm). A high correlation was found for soil temperature, evapotranspiration (ET), and surface temperature, respectively, in most of the stations at either a = 5 % or 1 %. All stations exhibited a downward trend in SM for the top three soil depths, whereas, for other depths some stations depicted an upward trend. From time series analysis, it was found that surface average temperature, ET and soil temperature varied on seasonal basis with maximum in June and minimum in January of each year. In addition, SM availability in the top 5 cm of soil depth showed more significance for having strong correlation with hydroclimatic variables and were essential in interpreting many hydrological processes. From analyses at shallow soil depths (5 and 10 cm), the spatial SM variability across the stations was consistent during winter and spring whereas inconsistent during summer and autumn. In addition, the SM exhibited a temporal cyclic variability for almost all stations.
Journal of the Korean Society of Hazard Mitigation
The current heatwave crisis alert system considers the daily maximum temperature alone; therefore... more The current heatwave crisis alert system considers the daily maximum temperature alone; therefore, the present study proposed a new method for estimating the daily heatwave crisis alert level. Specifically, the heatwave risk index was calculated by combining regional vulnerability, as estimated using principal component analysis, and normalized daily maximum temperature. The crisis alert level was classified according to the risk index value using the natural breaks method. The correlation coefficient between the heatwave risk index and heat-related morbidity rate was approximately 0.4. In addition, analysis of variance confirmed significant differences in the heat-related morbidity rate among different crisis alert levels. The current method is limited in that it does not take into account the various regional environmental characteristics, which may results in an ambiguous alert standard; however, this shortcoming may be resolved using the proposed heatwave risk index. Therefore, ...
KSCE Journal of Civil and Environmental Engineering Research, Dec 1, 2018
It is necessary to determine an optimal design frequency for establishing stable flood control ag... more It is necessary to determine an optimal design frequency for establishing stable flood control against frequent flood disasters. Depending on the importance of river and regional characteristics, design return periods are suggested from at least 50 years up to 200 years for river design. However, due to the wide range of applications, it is not desirable to reflect the geographical and flood control characteristics of river. In this study, Bayes theory was applied to seven evaluation factors to determine the optimal design return period of rivers in Chungcheongnam-do; urbanization flooded area, watershed area, basin coefficient, slope, water system and stream order, range of backwater effect, abnormal rainfall occurrence frequency. The potential flood damage (PFD) capacity was estimated considering climate change and the appropriate design return period was determined by analyzing the capacity of each district. We compared the design return periods of 382 rivers in Chungcheongnam-do with the existing design return periods. The number of rivers that were upgraded from the existing return period were 65, which have relatively large flooding areas and have large PFDs. Whereas, the number of rivers that were downgraded were 169.
Considering the effect of climate change, a quantitative analysis of extreme drought is needed to... more Considering the effect of climate change, a quantitative analysis of extreme drought is needed to reduce the damage from extreme droughts. Therefore, in this study, a quantitative risk analysis of extreme drought was conducted. The threshold level method was applied to define a drought event using Cheugugi rainfall data in past, gauged rainfall data in present, and climate change scenario rainfall data in future. A bivariate drought frequency analysis was performed using the copula function to simultaneously consider two major drought characteristics such as duration and severity. Based on the bivariate drought frequency curves, the risks for the past, present and future were calculated and the risks for future extreme drought were analyzed comparing with the past and present. As a result, the mean drought duration of the future was shorter than that of past and present, however, the mean drought severity was much larger. Therefore short term and severe droughts were expected to occur in the future. In addition, the analysis of the maximum drought risk indicated that the future maximum drought risk was 1.39~1.94 times and 1.33~1.81 times higher than the past and present. Finally, the risk of extreme drought over past and present maximum drought in the future was very high, ranging from 0.989 to 1.0, and the occurrence probability of extreme drought was high in the future.
Soil moisture is a crucial factor in hydrological system which influences runoff, energy balance,... more Soil moisture is a crucial factor in hydrological system which influences runoff, energy balance, evaporation, and atmosphere. United States National Aeronautic and Space Administration (NASA) and Department of Agriculture (USDA) have established Soil Moisture Experiment (SMEX) since 2002 for the global observations. SMEX provides useful data for the hydrological science including soil moisture and hydrometeorological variables. The purpose of this study is to investigate the relationship between remotely sensed soil moisture data from aircraft and satellite and ground based experiment. C-band of Polarimetric Scanning Radiometer (PSR) that observed the brightness temperature provides soil moisture data using a retrieval algorithm. It was compared with the In-situ data for 2-30 cm depth at four sites. The most significant depth is 2-10 cm from the correlation analysis. Most of the sites, two data are similar to the mean of data at 10 cm and the median at 7 cm and 10 cm at the 10% sig...
Rapid eye movement (REM) sleep without atonia (RSWA) fulfils one of the criteria for diagnosing R... more Rapid eye movement (REM) sleep without atonia (RSWA) fulfils one of the criteria for diagnosing REM sleep behavior disorder (RBD) according to the International Classification of Sleep Disorders, Third Edition. However, RSWA quantification is an unresolved issue, which is associated with the future direction of revising the diagnostic criteria. The purpose of this study was to evaluate the quantification of RSWA in patients with RBD and identify an optimal cutoff value of quantitative RSWA for RBD diagnosis. Methods: Medical records and polysomnographic results were analyzed retrospectively to diagnose sleep disorders from June 2017 to May 2018 at Pusan National University Hospital. Nineteen subjects with idiopathic RBD were included in the present study. Propensity score matching was used to control age, gender, and anti-depressant factors, which influenced RSWA. RSWA was scored according to the American Academy of Sleep Medicine scoring manual. Cohen's kappa coefficient was measured to test inter-rater reliability between two polysomnography raters. Results: Cohen's kappa coefficients were 0.755 (p<0.001) and 0.689 (p<0.001) for tonic and phasic activities, respectively. RSWA was significantly increased in subjects with RBD compared with controls [median and interquartile range: 16.5 (8.8-24.6) vs. 6.3 (4.1-7.2) p=0.001]. The optimal cutoff value was 8.0% for the proportion of RSWA (sensitivity 78.5%, specificity 85.7%, area under the receiver-operating characteristic curve 0.837). Conclusions: Subjects with RBD had significantly increased RSWA compared to controls. The proportion of RSWA during REM sleep can be applied to discriminate subjects with RBD from controls.
Journal of korean society of hazard mitigation, 2013
This paper sets forth key concepts and advances working definitions for sustainable and resilient... more This paper sets forth key concepts and advances working definitions for sustainable and resilient infrastructures (S&R-Infra), specifically for water systems. Three water infrastructure scales, such as large, medium, and small scales are considered, each of which is represented by water resource system, regional water and wastewater infrastructure, and local water distribution system, respectively. All three scales are interconnected each other since water travels from sources to end users and returns the other way. This study is beneficial by suggesting indicators to evaluate system sustainability and resilience against outer disturbances. After S&R definitions and potential indicators are provided, application examples are examined to demonstrate the applications of the proposed indicators. Application results show that the proposed indices are useful for quantifying water system performance. While the approach is refined and applied to synthetic cases, it may be considered applicable to real-world systems as system performance indicators and/or system planning and design goals within an optimization framework.
Due to the increased water demand and severe drought as an effect of the global warming, the effl... more Due to the increased water demand and severe drought as an effect of the global warming, the effluent from wastewater treatment plants becomes considered as an alternative water source to supply agricultural, industrial, and public (gardening) water demand. The effluent from the wastewater treatment plant is a sustainable water source because of its good quality and stable amount of water discharge. In this study, the water reuse system was developed to minimize total construction cost to cope with the uncertain water demand in future using two-stage stochastic linear programming with binary variables. The pipes in the water reuse network were constructed in two stages of which in the first stage, the water demands of users are assumed to be known, while the water demands in the second stage have uncertainty in the predicted value. However, the water reuse system has to be designed now when the future water demands are not known precisely. Therefore, the construction of a pipe parallel with the existing one was allowed to meet the increased water demands in the second stage. As a result, the trade-off of construction costs between a pipe with large diameter and two pipes having small diameters was evaluated and the optimal solution was found. Three scenarios for the future water demand were selected and a hypothetical water reuse network considering the uncertainties was optimized. The results provide the information about the economies of scale in the water reuse network and the long range water supply plan.
Journal of korean society of hazard mitigation, 2013
In Korea, the occurrence frequency of earthquakes has recently increased compared to the past. In... more In Korea, the occurrence frequency of earthquakes has recently increased compared to the past. In neighboring countries such as Japan and China, damage from major earthquakes has also increased leading to high earthquake risk. This study quantitatively estimated the occurrence probability and frequency of huge earthquake using statistical frequency analysis on instrumental earthquake data at East sea in order to cope with earthquake damage. After adapting Various distribution functions such as Gumbel, Lognormal, Gamma, and Weibull for earthquake data, we applied mixed distributions to reflect the characteristics of the occurrence of earthquakes. The results show that the mixed models estimated earthquake magnitude larger than the Gutenberg-Richter (G-R) equation, and the mixed Gumbel distribution estimated most closed values with the G-R equation. It was found that the G-R equation is very limited to estimate a huge earthquake since there is no observed data over magnitude 8.0 and the frequency analysis is also limited to be applied in practice because the lack of data induces high uncertainty on the estimates of 1,000 year-earthquake. However, this study has an experiential significance in that the statistical frequency analysis was applied to instrumental earthquake data at East sea as an alternative.
Journal of korean society of hazard mitigation, 2012
This study proposed a practical approach to estimate design rainfalls that can be applied to desi... more This study proposed a practical approach to estimate design rainfalls that can be applied to design reference year using the relationships among distribution parameters, annual rainfalls estimated from GCMs(Global Circulation Models), and annual maximum rainfalls observed at gauging stations, leading to consider climate change. The highlight of this study is to estimate distribution parameters through regression models with annual rainfalls as a causal factor. The proposed model was applied to estimated ensemble design rainfalls with 24-hr duration in built-up design reference years of 2020 and 2030 at 10 stations considering the uncertainty induced by emission scenarios and GCMs. The overall results indicated that the design rainfalls of Gangneung, Daejeon, Seoul, and Sokcho in 2020 and 2030 are higher than those in 2009(assumed as the current), the design rainfalls of Gwangju, Seosan, and Jeju in 2020 and 2030 are very close to the current, and the design rainfalls of Busan, Mokpo, and Daegu in 2020 and 2030 are lower than the current. It is considered that the trend component of the annual maximum rainfalls is incorporated into the process of estimating design rainfalls. The proposed method can provide design rainfalls in the next 10 more years in which the effect of climate change is reflected, and thus may suggest useful reference or alternatives for the hydrologic plan and management.
Accurate prediction of reservoir sediment inflows (Min) and adaptation of feasible sediment manag... more Accurate prediction of reservoir sediment inflows (Min) and adaptation of feasible sediment management strategies pose challenges in water engineering. This study proposed a two-stage complementary modeling approach for comprehensive reservoir sediment management. In the first stage, artificial neural network-based models provide real-time Min predictions using water inflow, water head, and outflow as input parameters. In the second stage, the parameter estimation method of the RESCON model is applied to hydraulic flushing in a reservoir. This approach was applied to the Sangju Weir and Nakdong River Estuary Barrage (NREB) in South Korea. Results from the RESCON model revealed that hydraulic flushing was effective for sediment management at both the Sangju Weir reservoir and the NREB approach channel. Efficient flushing at the Sangju Weir required a flushing discharge of 100 m3/s for 6 days and 40 m of water head. Efficient flushing at the NREB required a flushing discharge of 25 m3/s for 6 days with 1.8 m of water-level drawdown. The proposed approach is expected to prove useful in reservoir sediment management.
The soil-water interaction is crucial for effective hydrological processes determination. The soi... more The soil-water interaction is crucial for effective hydrological processes determination. The soil moisture (SM) is an important parameter to provide priori information for the interactions imparting and affecting the energy fluxes response for such kind of processes. This work investigated the effects of climatic, geophysical and hydrological parameters on SM at 9 stations within Utah State, USA, for daily data recorded between 2010 and 2012 at 5 different soil depths (approximately 5, 10, 20, 50, and 100 cm). A high correlation was found for soil temperature, evapotranspiration (ET), and surface temperature, respectively, in most of the stations at either a = 5 % or 1 %. All stations exhibited a downward trend in SM for the top three soil depths, whereas, for other depths some stations depicted an upward trend. From time series analysis, it was found that surface average temperature, ET and soil temperature varied on seasonal basis with maximum in June and minimum in January of each year. In addition, SM availability in the top 5 cm of soil depth showed more significance for having strong correlation with hydroclimatic variables and were essential in interpreting many hydrological processes. From analyses at shallow soil depths (5 and 10 cm), the spatial SM variability across the stations was consistent during winter and spring whereas inconsistent during summer and autumn. In addition, the SM exhibited a temporal cyclic variability for almost all stations.
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Papers by Tae-Woong Kim