• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2015년도 학술발표회
• /
• pp.235-235
• /
• 2015

This study investigates the impact of event characteristics on runoff dynamics during extreme flood events observed in a $8.5km^2$ experimental watershed located in South Korea. The 37 most extreme flood events with event rainfall in excess of 50 mm were analysed using an event-based rainfall-runoff model; the Revitalised Flood Hydrograph (ReFH) routinely used for design flood estimation in the United Kingdom. The ReFH model was fitted to each event in turn, and links were investigated between each of the two model parameters controlling runoff production and response time, respectively, and event characteristics such as rainfall depth, duration, intensity and also antecedent soil moisture. The results show that the structure of the ReFH model can effectively accommodate any nonlinearity in runoff production, but that the linear unit hydrograph fails to adequately represent a reduction in watershed response time observed for the more extreme events. By linking the unit hydrograph shape directly to rainfall depth, the consequence of the observed nonlinearity in response time is to increase design peak flow by between 50% for a 10 year return period, and up to 80% when considering the probable maximum flood (PMF).

• 한국수자원학회:학술대회논문집
• /
• 한국수자원학회 2015년도 학술발표회
• /
• pp.537-537
• /
• 2015

In recent decades, the independence and identical distribution (iid) assumption for extreme events has been shown to be invalid in many cases because long-term climate variability resulting from phenomena such as the Pacific decadal variability and El Nino-Southern Oscillation may induce varying meteorological systems such as persistent wet years and dry years. Therefore, in the current study we propose a new parameter estimation method for probability distribution models to more accurately predict the magnitude of future extreme events when the iid assumption of probability distributions for large-scale climate variability is not adequate. The proposed parameter estimation is based on a metaheuristic approach and is derived from the objective function of the rth power probability-weighted sum of observations in increasing order. The combination of two distributions, gamma and generalized extreme value (GEV), was fitted to the GEV distribution in a simulation study. In addition, a case study examining the annual hourly maximum precipitation of all stations in South Korea was performed to evaluate the performance of the proposed approach. The results of the simulation study and case study indicate that the proposed metaheuristic parameter estimation method is an effective alternative for accurately selecting the rth power when the iid assumption of extreme hydrometeorological events is not valid for large-scale climate variability. The maximum likelihood estimate is more accurate with a low mixing probability, and the probability-weighted moment method is a moderately effective option.

• Wind and Structures
• /
• 제15권2호
• /
• pp.177-188
• /
• 2012

The meteorological events that cause most strong winds in Brazil are extra-tropical cyclones, downbursts and tornadoes. However, one hurricane formed off the coastline of southern Brazil in 2005, a tropical storm formed in 2010 and there are predictions that others may form again. Events such as those described in the paper and which have occurred before 1987, generate data for the wind map presented in the Brazilian wind loading code NBR-6123. This wind map presents the reference wind speeds based on 3-second gust wind speed at 10 m height in open terrain, with 50-year return period, varying from 30 m/s (north half of country) to 50 m/s (extreme south). There is not a separation of the type of climatological event which generated each registered velocity. Therefore, a thunderstorm (TS), an extra-tropical pressure system (EPS) or even a tropical cyclone (TC) are treated the same and its resulting velocities absorbed without differentiation. Since the flow fields generated by each type of meteorological event may be distinct, the indiscriminate combination of the highest wind velocities with aerodynamic coefficients from boundary layer wind tunnels may lead to erroneous loading in buildings.

• Geomechanics and Engineering
• /
• 제22권5호
• /
• pp.433-439
• /
• 2020

Tunnels are one of the most important constructions in civil engineering. The damage to these structures caused enormous costs. Therefore, the safe and economic design of these structures has long been considered. However, both applied loads on the tunnels as well as the resistance of the structural members are naturally uncertain parameters, hence, the design of these structures requires considering the probabilistic approaches. This study aims to determine the load and resistant factors of lining tunnels concerning the earthquake extreme events limit state function. For this purpose, tunnels that have been designed according to the previous design codes (AASHTO Tunnel LRFD 2017) and using reliability analysis, the optimum reliability of these structures for different loading scenarios is determined. In this paper, the tunnel is considered circular. Finally, the proper load and resistance factors are calculated corresponding to the obtained target reliability. Based on the performed calibration earthquake extreme events limit state function, the result of this study can be recommended to AASHTO Tunnel LRFD 2017.

• 한국수산과학회지
• /
• 제41권4호
• /
• pp.294-300
• /
• 2008

Abnormal cooling of the Korean East Sea Water(KESW) in the East Sea before and after the 1982-1983 and 1997-1998 ENSO events is examined using bimonthly routine observation data from the National Fisheries Research and Development Institute of Korea for the period 1965 to 2002. The KESW, which occupies roughly a region between the Korean Peninsula and west of approximately $131^{\circ}E$, showed extreme cold-state years(1981 and 1996) prior to the two strongest ENSO events of the last half-century. Inter-annual bimonthly mean anomalies at 100 m in the KESW region were $-3.10^{\circ}C\;and\;-3.41^{\circ}C(SD=1.4^{\circ}C)$ in 1981 and 1996, respectively. These results suggest that extreme cooling of the KESW may be a prelude to very strong ENSO events through large-scale teleconnections.

• 한국지역지리학회지
• /
• 제20권4호
• /
• pp.393-408
• /
• 2014

본 연구에서는 우리나라 여름철 극한강수현상 발생의 시 공간적 특성을 밝히고자 하였다. 분석에 사용된 자료는 최근 10년간(2002~2011년) 기상청 산하 전국 약 360여개 방재기상관측장비 및 종관기상관측장비의 일강수량 자료이다. 일강수량 80mm 이상의 극한강수현상과 일강수량 극값은 여름장마기(6월 하순~7월 중순)에 전국적으로 높게 나타났지만, 장마전선이 북상하는 장마휴지기(7월 하순~8월 초순)에는 경기북부~강원 영서 북부 지역에, 장마전선이 남하하는 늦장마기(8월 중순~9월 초순)에는 경기도~강원 영서 남부 지역 및 지리산, 한라산 주변지역에서 높게 나타났다. 세부 지역별로 극한강수현상의 발생빈도와 극값 분포를 살펴보면, 종관규모인 장마전선의 위치뿐만 아니라 해발고도와 사면의 방향성과 같은 지형요소와 기류의 유입 등이 극한기후현상의 시 공간성에 영향을 미치는 기후인자임을 알 수 있었다. 이러한 결과는 우리나라 각 지역과 여름철 시기별로 상이하게 나타나는 극한강수현상의 발생빈도와 강도를 고려하여 지역별로 차별화된 호우 피해 저감 대책이 필요함을 시사한다.

• 한국지역지리학회지
• /
• 제19권3호
• /
• pp.384-400
• /
• 2013

이 연구에서는 기상청 종관기상관측망 및 자동기상관측망의 약 340여개의 일별 강수 관측자료를 바탕으로 최근 10년간(2002~2011년) 평균 우리나라 태풍 내습 시 극한강수현상 발생의 시 공간적 패턴을 분석하였다. 일반적으로 태풍에 의한 일 강수량 80mm 이상 극한강수현상 발생빈도는 태풍의 길목에 해당하는 제주도 이외에도 경상남도 지역과 영동 해안지역에 높게 나타난다. 그러나 수백 km 이상 반경을 지닌 반시계 방향의 수증기 이류가 나타날 때 태풍 내습 경로 및 접근 거리별로 우리나라 주요 산맥에 의해 수증기 이류정도가 변하여 극한강수현상 발생빈도, 강도 및 그 범위가 달라진다. 7월에 발생빈도가 높은 황해 북상형 태풍 내습 시에는 남해안지역과 영동해안지역 이외에도 경기도 북부지역에 극한강수현상의 발생빈도가 높게 나타남을 알 수 있다. 8월~9월 초로 갈수록 발생확률이 높아지는 한반도 남부지역 상륙형 및 동해 북상형 태풍 내습 시에는 남해안 및 영동해안지역뿐만 아니라 경상남도 내륙지역에서도 극한강수현상 발생빈도가 높게 나타난다. 특히, 해발고도가 높은 한라산, 지리산 지역에서는 태풍 내습 시 많은 강수량을 초래하는 극한강수현상이 자주 발생함을 알 수 있다. 이러한 연구 결과들은 태풍 이동경로 및 접근거리에 따라 지역별로 차별화된 태풍 피해 저감대책을 마련할 필요성을 제시하고 있다.

• Communications for Statistical Applications and Methods
• /
• 제25권1호
• /
• pp.15-27
• /
• 2018

Parametric method of flood frequency analysis involves fitting of a probability distribution to observed flood data. When record length at a given site is relatively shorter and hard to apply the asymptotic theory, an alternative distribution to the generalized extreme value (GEV) distribution is often used. In this study, we consider the beta-P distribution (BPD) as an alternative to the GEV and other well-known distributions for modeling extreme events of small or moderate samples as well as highly skewed or heavy tailed data. The L-moments ratio diagram shows that special cases of the BPD include the generalized logistic, three-parameter log-normal, and GEV distributions. To estimate the parameters in the distribution, the method of moments, L-moments, and maximum likelihood estimation methods are considered. A Monte-Carlo study is then conducted to compare these three estimation methods. Our result suggests that the L-moments estimator works better than the other estimators for this model of small or moderate samples. Two applications to the annual maximum stream flow of Colorado and the rainfall data from cloud seeding experiments in Southern Florida are reported to show the usefulness of the BPD for modeling hydrologic events. In these examples, BPD turns out to work better than $beta-{\kappa}$, Gumbel, and GEV distributions.

• 대한토목학회논문집
• /
• 제43권6호
• /
• pp.699-708
• /
• 2023

원자력 발전소는 안전하게 운영될 수 있도록 설계단계에서 자연재해를 포함한 예상 가능한 모든 외부사건들이 고려되고 있다. 그러나 최근에 기후변화로 인해 설계를 초과하는 자연재해의 발생 가능성이 증가하면서 설계 당시에 예측하지 못했던 극한자연재해와 외부사건에 대해 세심한 검토가 요구되고 있다. 본 연구에서는 국내 원전 부지별 잠재적 극한자연재해를 선별하고자 하였다. 이를 위해서 원전 부지특성과 원전 부지별 외부재해로 인해 발생한 사건을 조사하고 분석하였다. 그리고 기존 문헌과 연구 자료를 조사하여 국내 원전 실정에 맞는 선별절차와 기준을 수립하였다. 본 연구에서 수립된 선별기준에 근거하여 원전 부지별로 정성적 선별을 수행하였고, 선별된 자연재해를 대상으로 정량적 선별과 현장실사를 통해 국내 원전 부지별 잠재적 극한자연재해를 선별하였다. 선별 결과, 폭우에 의한 내부침수 이외에도 강풍에 의한 풍압과 극한 공기압이 모든 부지에서 공통적인 잠재적 극한자연재해로 선별되었다. 그리고 고리부지의 경우 폭풍해일이 1순위의 잠재적 극한자연재해로 선정되었다.

• Journal of the Korean Data and Information Science Society
• /
• 제26권2호
• /
• pp.535-545
• /
• 2015

In a various range of applications including hydrology, the type-I extreme value distribution has been extensively used as a probabilistic model for analyzing extreme events. In this paper, we introduce methods for estimating the scale parameter of the type-I extreme value distribution. A simulation study is performed to compare the estimators in terms of mean-squared error and bias, and the obtained results are provided.