Soonyoung Yu

Quantitative assessment of disaster resilience: An empirical study on the importance of post-disaster recovery costs

Recovery costs are as important as losses for decision-making in disaster mitigation given that recovery costs reflect the restorative capacity of affected regions. Hence, this study analyses recovery costs. Results show that the total post-disaster recovery costs in Korea are on average one and a half times the actual losses, mainly because of the private sector. This ratio depends on the hazard type. In Korea, the highest ratio (almost four) arises after heavy rains because of the weak restorative capacity of river systems to heavy rains. The study introduces the community resilience cost index (CRCI), obtained by adding recovery costs and losses and dividing the resultant sum by the magnitude of exposure levels to quantify national and regional resilience. Results show that the recovery cost is an essential component for assessing resilience. In particular, the high ratio of recovery costs to losses owing to heavy rains changes the priorities determined by losses only. The key contribution of this work is that the ratios between losses and recovery costs can estimate the recovery costs based on losses given the high correlation. The study ascertains the most vulnerable system and explains why this is so through analyzing the recovery costs. The importance of recovery costs in quantitative resilience assessments is exemplified. Last, the CRCI is transferrable to other countries to assess their resilience and to establish their priorities and vulnerabilities.

Groundwater contamination with volatile organic compounds in urban and industrial areas: analysis of co-occurrence and land use effects

Chlorinated solvents and trihalomethanes were the most frequently detected volatile organic compound (VOC) groups in groundwater in two metropolitan cities and three industrial complexes in Korea. Groundwater contamination with carbon tetrachloride and chloroform was noticeable in the industrial complexes, while MTBE was frequently detected only in metropolitan cities. In particular, groundwater was severely contaminated with chlorinated solvents and their dechlorination intermediates, including cis-1,2-DCE from TCE and 1,1-DCE from 1,1,1-TCA. Their co-occurrences were analyzed based on detection frequencies, rates of exceeding the water quality criteria, and a correlation matrix. Meanwhile, frequently co-occurring VOCs and VOC concentrations exceeding the water quality criteria were detected in only a few samples, which demonstrates the effects of land use due to the application of various types of VOCs. Thus, the effects of local land use were investigated by categorizing groundwater samples based on land use at the sampling locations; the effects of regional land use were assessed using factor analysis with administrative district statistics. The assessment results showed that public garages at the sampling locations were correlated with groundwater contamination. The detection of MTBE was correlated with vehicle use, while the detection of both toluene and chloroform was correlated with manufacturing and sewage collection and disposal systems; PCE was correlated with hazardous wastes. The contribution of this work is that the co-occurrence of some VOCs and persistent dechlorination intermediates was analyzed using a correlation matrix. Local and regional land uses were separately defined; their impacts on groundwater quality were assessed. Furthermore, a factor analysis included anthropogenic variables and VOC detection rates to better define latent variables.

Lead isotopes combined with a sequential extraction procedure for source apportionment in the dry deposition of Asian dust and non-Asian dust.

Lead isotopic compositions were determined in leachates that were generated using sequential extractions of dry deposition samples of Asian dust (AD) and non-Asian dust (NAD) and Chinese desert soils, and used to apportion Pb sources. Results showed significant differences in (206)Pb/(207)Pb and (206)Pb/(204)Pb isotopic compositions in non-residual fractions between the dry deposition samples and the Chinese desert soils while (206)Pb/(207)Pb and (206)Pb/(204)Pb isotopic compositions in residual fraction of the dry deposition of AD and NAD were similar to the mean (206)Pb/(207)Pb and (206)Pb/(204)Pb in residual fraction of the Alashan Plateau soil. These results indicate that the geogenic materials of the dry deposition of AD and NAD were largely influenced by the Alashan Plateau soil, while the secondary sources of the dry deposition were different from those of the Chinese desert soils. In particular, the lead isotopic compositions in non-residual fractions of the dry deposition were homogenous, which implies that the non-residual four fractions (F1 to F4) shared the primary anthropogenic origin. (206)Pb/(207)Pb values and the predominant wind directions in the study area suggested that airborne particulates of heavily industrialized Chinese cities were one of the main Pb sources. Source apportionment calculations showed that the average proportion of anthropogenic Pb in the dry deposition of AD and NAD was 87% and 95% respectively in total Pb extraction, 92% and 97% in non-residual fractions, 15% and 49% in residual fraction. Approximately 81% and 80% of the anthropogenic Pb was contributed by coal combustion in China in the dry deposition of AD and NAD respectively while the remainder was derived from industrial Pb contamination. The research result proposes that sequential extractions with Pb isotope analysis are a useful tool for the discrimination of anthropogenic and geogenic origins in highly contaminated AD and NAD.

Lead chromate detected as a source of atmospheric Pb and Cr (VI) pollution

Spherical black carbon aggregates were frequently observed in dust dry deposition in Daejeon, Korea. They were tens of micrometers in diameter and presented a mixture of black carbon and several mineral phases. Transmission electron microscopy (TEM) observations with energy-dispersive X-ray spectroscopy (EDS) and selected area diffraction pattern (SADP) analyses confirmed that the aggregates were compact and included significant amounts of lead chromate (PbCrO4). The compositions and morphologies of the nanosized lead chromate particles suggest that they probably originated from traffic paint used in roads and were combined as discrete minerals with black carbon. Based on Pb isotope analysis and air-mass backward trajectories, the dust in Daejeon received a considerable input of anthropogenic pollutants from heavily industrialized Chinese cities, which implies that long-range transported aerosols containing PbCrO4 were a possible source of the lead and hexavalent chromium levels in East Asia. Lead chromate should be considered to be a source of global atmospheric Pb and Cr(VI) pollution, especially given its toxicity.

Creating an advanced backpropagation neural network toolbox within GIS software

An artificial neural network (ANN) toolbox is created within GIS software for spatial interpolation, which will help GIS users to train and test ANNs, perform spatial analysis, and display results as a single process. The performance is compared to that of the open source Fast Artificial Neural Network library and conventional interpolation methods by creating digital elevation models (DEMs) given that nearly exact solutions exist. Simulation results show that the advanced backpropagations such as iRprop speed up the learning, while they can get stuck in a local minimum depending on initial weight sets. Besides, the division of input–output examples into training and test data affects the accuracy, particularly when the distribution of the examples is skewed and peaked, and the number of data is small. ANNs, however, show the similar performance to inversed distance weighted or kriging and outperform polynomial interpolations as a global interpolation method in high-dimensional data. In addition, the neural network residual kriging (NNRK) model, which combines the ANN toolbox and kriging within GIS software, is performed. The NNRK outperforms conventional methods and well captures global trends and local variations. A key outcome of this work is that the ANN toolbox created within the de facto standard GIS software is applicable to various spatial analysis including hazard risk assessment over a large area, in particular when there are multiple potential causes, the relationship between risk factors and hazard events is not clear, and the number of available data is small given its performance for DEM generation.

An accurate multidimensional limiter on quadtree grids for shallow water flow simulation

ABSTRACT In hydraulic research, numerical modelling of complex flows is essential for managing water risks. High-resolution finite volume schemes have become popular for shallow water flow modelling due to their mass and momentum balance characteristics and their ability to capture shocks. These methods use slope limiters to suppress numerical oscillations near discontinuities. However, one-dimensional limiters do not assure numerical accuracy in multidimensional applications, occasionally leading to excessive or insufficient numerical dissipation. For this reason, a multidimensional limiting process (MLP) was developed for oscillation control in multidimensional compressible flows. In this paper, we implement MLP on adaptive quadtree grids for shallow water flow simulations and compare MLP performance with simulations using conventional limiters. Four simulation cases show that MLP outperforms conventional limiters, and yield more accurate and stable solutions on adaptive quadtree grids. The capability of MLP for oscillation control is more noticeable on quadtree than on uniform grids.

Research Methodology for the Economic Impact Assessment of Natural Disasters and Its Applicability for the Baekdu Mountain Volcanic Disaster

There are many studies for the economic impact assessment of natural disasters, but there are few for volcanic disasters. Domestic academic research is not under active discussion because of the lack of national and social interest for volcanic eruption. This study investigated the research methodology for the economic impact assessment of natural disasters and discussed whether these can be applied to the economic impact analysis for the Baekdu Mountain volcanic disaster. The main findings are as follows: Firstly, Asia-Pacific region is the most affected by natural disasters and has the largest scale of damage. Asian and American Continent have the most economic damage. Secondly, Considering the types of damage caused by natural disasters and its complex structure, several methodologies that could be possible to estimate economic consequential damages have been compared. When applying each methodology to the Baekdu Mountain volcanic disaster, the scale of damage is likely to be over-estimated or under-estimated because of model-specific features. Thus, estimated values should be compared to each other after calculating the damage results. Thirdly, Japanese academic research on the volcanic disaster will be used as the starting point of the economic impact assessment studies for Baekdu Mountain. Using computer SW such as Hazus which is used in United States and RiskScape from New Zealand is also a good method to predict economic impact of the Baekdu Mountain volcanic disaster.

Building Damage Functions Using Limited Available Data for Volcanic Ash Loss Estimation

Catastrophe risk models require the damage functions of each vulnerable item in inventory to estimate volcanic ash losses. The damage functions are used to represent the relation between damage factors and damage and also widely used in engineering and natural hazard studies to calculate the vulnerability. In most cases, damage functions are constructed as fragility or vulnerability curves, and researchers are confused by the similarities between them particularly when they perform interdisciplinary research. Thus, we aim to explain the similarities and differences between fragility and vulnerability curves and their relationship by providing case studies to construct them. In addition, we suggest a simple method to construct the damage functions between damage ratio and volcanic ash thickness using limited damage data. This study comes from the fact that damage functions are generally constructed using damage data. However, there is no available volcanic ash damage data in Korea, and not even enough volcanic disaster data to construct damage functions in the world, compared to other hazards. Using the method suggested in the study and the limited damage data from Japan and New Zealand, we construct Weibull-type functions or linear functions dependent of available data to calculate volcanic ash loss estimation, which we think need to be corrected to make it more suitable for inventory characteristics and environmental conditions in Korea.

Numerical Simulation of Urban Flash Flood Experiments Using Adaptive Mesh Refinement and Cut Cell Method

Two-dimensional shallow water model based on the cut cell and the adaptive mesh refinement techniques is presented in this paper. These two mesh generation methods are combined to facilitate modeling of complex geometries. By using dynamically adaptive mesh, the model can achieve high resolution efficiently at the interface where flow changes rapidly. The HLLC Reimann solver and the MUSCL method are employed to calculate advection fluxes with numerical stability and precision. The model was applied to simulate the extreme urban flooding experiments performed by the IMPACT (Investigation of Extreme Flood Processes and Uncertainty) project. Simulation results were in good agreement with observed data, and transient flows as well as the impact of building structures on flood waves were calculated with accuracy. The cut cell method eased the model sensitivity to refinement. It can be concluded that the model is applicable to the urban flood simulation in case the effects of sewer and stormwater drainage system on flooding are relatively small like the dam brake.

Forecasting the Unit Price of Water and Wastewater Pipelines Capital Works and Estimating Contractors’ Markup

Municipalities and water utilities need to make realistic estimates for the replacement of their aged water and wastewater pipelines. The two main objectives of this article are to present a method to forecast the unit price of water and wastewater pipelines capital works by investigating inflation in their construction price, and to quantify the markup that contractors add to bid a project price. The Geometric Brownian Motion model with drift is used for investigation. Results show that the inflation in water and wastewater pipelines reference projects were 6.41% and 5.52% per annum, respectively. These values compare to the inflation in the Standard & Poor’s/Toronto Stock Exchange (S&P/TSX) Composite Index of 6.93% per annum. In contrast, inflation in Canada’s Consumer Price Index (CPI), and Engineering News-Record’s Construction Cost Index (ENR’s CCI) for Toronto are estimated to be 2.53% and 2.85% per annum, respectively. The spread in the inflation rate between the reference price indices and that of either ENR’s CCI or CPI is a measure of the market price of catchall financial premium (defined as markup) that contractors add to project cost to account for profit, risk, and market conditions. This spread is estimated to be 3.56% and 2.67% per annum for water and wastewater pipeline capital works, respectively.