Sun-Kwon Yoon

Application to Evaluation of Hydrologic Time Series Forecasting for Long-Term Runoff Simulation

Hydrological system forecasting, which is the short term runoff historical data during the limited period in dam site, is a conditional precedent of hydrological persistence by stochastic analysis. We have forecasted the monthly hydrological system from Andong dam basin data that is the rainfall, evaporation, and runoff, using the seasonal ARIMA (autoregressive integrated moving average) model. Also we have conducted long term runoff simulations through the forecasted results of TANK model and ARIMA+TANK model. It has been taking for three steps, which is model identification, model estimation and model diagnostic checking, to modeling for time series data to processing typical Box and Jenkins method. Therefore, time series data analysis carry out the model distinguished from ACF (autocorrelation function), PACF (partial autocorrelation function), AIC (akaike’s bayesian criterion) and SBC (schwartz’s bayesian criterion). Model diagnostic checking has been performed to portmanteau test, residual test and model identification by ML (maximum likelihood) method. The results of analysis have been concurred to the observation data, and it has been considered for application to possibility on the stochastic model for dam inflow forecasting. Thus, the method presented in this study suggests a help to water resource mid- and long-term strategy establishment to application for runoff simulations through the forecasting variables of hydrological time series on the relatively short holding runoff data in an object basins.

A Study on Optimal Time Distribution of Extreme Rainfall Using Minutely Rainfall Data: A Case Study of Seoul

In this study, we have developed an optimal time distribution model through extraction of peaks over threshold (POT) series. The median values for annual maximum rainfall dataset, which are obtained from the magnetic recording (MMR) and the automatic weather system(AWS) data at Seoul meteorological observatory, were used as the POT criteria. We also suggested the improved methodology for the time distribution of extreme rainfall compared to Huff method, which is widely used for time distributions of design rainfall. The Huff method did not consider changing in the shape of time distribution for each rainfall durations and rainfall criteria as total amount of rainfall for each rainfall events. This study have suggested an extracting methodology for rainfall events in each quartile based on interquartile range (IQR) matrix and selection for the mode quartile storm to determine the ranking cosidering weighting factors on minutely observation data. Finally, the optimal time distribution model in each rainfall duration was derived considering both data size and characteristics of distribution using kernel density function in extracted dimensionless unit rainfall hyetograph.

Impacts of Two Types of El Niño on Hydrologic Variability in Annual Maximum Flow and Low Flow in the Han River Basin

In this study, we analysed hydrologic variability in quantity and onset of annual maximum flow and low flow by impacts of the different phases of ENSO (El Nio Southern Oscillation) over the Han River Basin. The results show that annual maximum flow has increased statistically significant about 48.3% of all over the watershed. The onset of annual maximum flow was delayed in the west of the Han River basins and in the east of the basins was likely to be rapid onset. Also, this study shows that 7-day low flow was deceased statistically significant about 26.0% of the total area in the Han River Basin, and onset of 7-day low flow tends to be faster in the upper-middle basins of the Han River. The onset of annual maximum flow shows similar pattern during the CT (Cold tongue)/WP (Warm-pool) El Nio years, but annual maximum flow appeared less in 89.0% of all basins during the CT El Nio years. In addition, the onset of 7-day low flow tended to be faster about 17 days on average during the WP El Nio years, and 72.7% of the basins show significant increase during the CT El Nio years. Consequently, it was found that the different phases of CT/WP El Nio have effects on sensitivity to variability in quantity and onset of water resources over the Han River Basin. We expect that the present diagnostic study on hydrological variability during different phases of ENSO will provide useful information for long-term prediction and water resources management.

Changes in Typhoon Activities and Regional Precipitation Variability over the Korean Peninsula according to Different Phases of El Niño

We analyzed typhoon activities such as tropical cyclone (TC) genesis position, movement routes and central pressure of typhoons, and changes in local patterns of rainfall stemming from TCs passing through the Korean domain. The results showed a remarkable difference in changes in typhoons that affect the Korean Peninsula (KP) during cold tongue (CT) and warm pool (WP) El Nino years. In particular, TCs that move through the ocean off Korea and the Kuroshio during WP El Nino years are relatively stronger than TCs formed during CT El Nino years. Furthermore, analysis of large-scale atmosphere-ocean dynamics showed better conditions for TC development and strengthening during WP El Nino years. TC-induced summer rainfall over major Korean river basins decreased from normal years during CT El Nino years (−3.94%) and increased over normal years during WP El Nino years (

Different Impacts of the Two Phases of El Niño on Variability of Warm Season Rainfall and Frequency of Extreme Events over the Han River Basin

This study investigated impacts of the two different types of El Nio on summer rainfall (June-September) in the Han River and its sub-basins. The patterns of rainfall anomalies show a remarkable difference between conventional El Nio and El Nio Modoki years. During conventional El Nio years, it was found that the Han River basins show decreases in the seasonal rainfall totals with high variations (CV

Analysis of Hydraulic effects on Piers and Transverse Overflow Type Structures in Urban Stream

Recently, stream flow analysis has been accomplished by one or two dimensional equations and was applied by simple momentum equations and fixed energy conservations which contain many condition limits. In this study, FLOW-3D using CFD (Computational Fluid Dynamics) was applied to stream flow analysis which can solve three dimensional RANS (Reynolds Averaged Navier-Stokes Equation) control equation to find out physical behaviors and the effect of hydraulic structures. Numerical simulation accomplished those results was compared by using turbulence models such as   , RNG (Renormalized Group)    and LES (Large Eddy Simulation). Numerical analysis results have been illustrated by the turbulence energy effects, velocity of flow, water level pressure and eddy flows around the piers and transverse overflow type structures. These results will be able to used by basis data that catch hold of effects on long-term bed elevation changes, sediment accumulations, scours and water aggravations by removal of obsolete transverse over flow type structures in urban stream. keywords : FLOW-3D, Turbulence Model, Transverse overflow type structure, Urban stream ..............................................................................................................................................................................................

The Uncertainty of Extreme Rainfall in the Near Future and its Frequency Analysis over the Korean Peninsula using CMIP5 GCMs

This study performed prediction of extreme rainfall uncertainty and its frequency analysis based on climate change scenarios by Coupled Model Intercomparison Project Phase 5 (CMIP5) for the selected nine-General Circulation Models (GCMs) in the near future (2011-2040) over the Korean Peninsula (KP). We analysed uncertainty of scenarios by multiple model ensemble (MME) technique using non-parametric quantile mapping method and bias correction method in the basin scale of the KP. During the near future, the extreme rainfall shows a significant gradually increasing tendency with the annual variability and uncertainty of extreme ainfall in the RCP4.5, and RCP8.5 scenarios. In addition to the probability rainfall frequency (such as 50 and 100-year return periods) has increased by 4.2% to 10.9% during the near future in 2040. Therefore, in the longer-term water resources master plan, based on the various climate change scenarios (such as CMIP5 GCMs) and its uncertainty can be considered for utilizing of the support tool for decision-makers in water-related disasters management.

Validation of Multi-satellite Precipitation Products for Assessing their Potential Utility of Hydrological Application Over South Korea

Multi-satellite precipitation products can provide possible opportunity for diverse hydrological applications in Korea. This study investigated the potential utility of three multi-satellite precipitation estimates, including TRMM(Tropical Rainfall Measuring Mission) 3B42v6, CMORPH(Climate Prediction Center Morphing), and GSMaP(Global Satellite Mapping of Precipitation)-MVK(Moving Vector with Kalman filter), from 2002 to 2009 by comparing with ground-gauged precipitation data over four major river basins of South Korea. The results showed that the frequency and amount of TRMM 3B42v6 estimates agreed well with observations at daily scale. However, CMORPH and GSMaP-MVK exhibited relatively poor performance than TRMM 3B42v6 with significantly underestimated precipitation. Overall, our results were consistent across four major river basins.

Atmospheric Circulation of Pacific-Japan (PJ) and Typhoon-induced Extremes in the Nakdong River Basin

The East Asia (EA) region including China, Taiwan, Japan, and Korea are especially vulnerable to hydrometerological extremes during the boreal summer (June-September). Therefore, this study pursued an exploratory analysis to improve better understanding of the potential impacts of the PJ pattern on WNP Tropical cyclone (TC) activity and TC-affected extremes based on the Korean Nakdong River Basin. The results show that during the positive PJ years, the large-scale atmospheric environments tend more favorable for the TC activity than those in the negative PJ years. KP-influenced TCs during the positive (negative) PJ years are likely to occur more southwestward (northeastward), recurve at more northwestward (northeastward) locations, and indicate increase (decrease) in frequency over Korea and Japan. Consequently, TCs making landfall are more exhibited over the southeastern portions of South Korea during the positive PJ years.

Development of a Time-Temperature Indicating Device Using Phospholipase

As an attempt to create a lime-temperature indicator (TTI) which performs reproducible reaction with confidence in monitoring storage life of frozen foods, a TTI using phospholipase was developed and applicability of the TTI to frozen pork was investigated. Smaller standard deviations of the reaction rate constants for phospholipase system over the temperature range between 30°C and -18°C than those for lipase system indicated that the former is more reliable than the latter. Good correlation between the color change of the TTI and the TBA value of frozen pork at fluctuating storage temperature suggested the potentiality of the TTI for predicting the storage life of frozen foods.