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Probabilistic solution to soil water evaporated flow equation
김상단 대한토목학회 2006 KSCE JOURNAL OF CIVIL ENGINEERING Vol.10 No.1
re.The newly developed model has the form of the Fokker-Planck equation, and its validity as a model for the probabilistic evolution ofthe nonlinear stochastic unsaturated flow process is investigated under a stochastic soil-related parameter (i.e., saturated hydraulicconductivity). This model is based on a parabolic type of stochastic partial differential equation, and has the advantage of providingthe probabilistic solution in the form of a probability distribution function, from which one can obtain the ensemble average behaviorof the flow system. The comparison results with Monte Carlo simulations show that the proposed model can reproduce well thevertically varying soil water wetting front depth. Overall, the ensemble averaging approach using the cumulant expansion method
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개념적인 토양수분 모의모형을 이용한 미래 극한 가뭄사상의 시공간적 해석
김상단,이야연,이재운,김태웅 한국방재학회 2011 한국방재학회논문집 Vol.11 No.6
본 연구에서는 현재 및 미래기후에서의 가뭄심도-영향면적-지속기간 곡선의 비교를 통하여 극한 가뭄사상의 시공간적 거동에대한 기후변화의 영향을 살펴보았다. 미래의 기온상승경향을 고려하기 위하여 표준토양수분지수가 제안된다. 표준토양수분지수는일평균기온과 일강수량 자료가 반영된 개념적인 토양수분모형으로부터 산출된다. 미래기후는 CGCM3.1-T63과 CSIRO-MK3.0으로부터 획득되었다. 분석 결과 CGCM3.1-T63 및 CSIRO-MK3.0 모두 미래가뭄이 현재보다 더 극심해질 것으로 예측되었다. 이에 따라 현재의 수자원 공급 시스템에 대한 기후변화 취약성 평가가 시급함을 제시하고 있다. In this study, the impact of climate change on the spatio-temporal behavior of extreme drought events is investigated by comparing drought severity-area-duration curves under present and future climate conditions. In order to consider future increasing trends in air temperature, the standardized soil water index is introduced. The standardized soil water index is calculated using a conceptual soil water model forced by daily air temperature and daily precipitation data. In our climate-change impact experiments,the future climate is based on two GCMs(CGCM3.1-T63 and CSIRO-MK3.0). As a result, in both cases of CGCM3.1-T63and CSIRO-MK3.0 the future drought risk is likely to increase. Such results indicate that a climate change vulnerability assessment for present water resources supply system is urgent.
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단순회귀모형을 이용한 인구와 도시적 토지이용이 팔당호 수질에 미치는 영향 분석
김상단,송미영,이기영,이성룡 한국물환경학회 2004 한국물환경학회지 Vol.20 No.6
In this study, a simple regression model is proposed in order to analyse the effect of population and urban land use on the water quality of Paldang lake, Gyeonggi. As a comparison result with Qua12E water quality model, the proposed model shows very good predicting performance in simulating several alternative scenarios. In order to accomplish BOD 1ppm of Paldang lake, various model applications show that the population incoming and urban land use management should be afoot in addition to stricter outflow water quality from sewer treatmement systems.
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Probabilistic Solution to Stochastic Infiltrated Flow Equation
김상단,윤용남,윤재영,장수형 대한토목학회 2004 KSCE JOURNAL OF CIVIL ENGINEERING Vol.8 No.6
Unsaturated flow with heterogeneous soil surfaces in the field scale is an outstanding issue in hydrologic modeling. The objective of this study is to develop and solve the upscaling conservation equation, which has the form of the Fokker-Planck equation. In this study, the impact of areal heterogeneity of soil hydraulic parameter on soil ensemble behavior during constant rainfall was examined. Field variability is assumed to take place in the horizontal plane. The results from the upscaling of one-dimensional vertical unsaturated flow model are compared with extensive sets of Monte-Carlo simulations for several degrees of the heterogeneity in soil surfaces. The application results of the upscaling model reveal that the upscaling model provides an adequate estimate of field scale soil moisture behavior in terms of its probability density distribution as well as its ensemble behavior.
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Wavelet Analysis of Precipitation Variability in Northern California, U.S.A.
김상단 대한토목학회 2004 KSCE JOURNAL OF CIVIL ENGINEERING Vol.8 No.4
Precipitation temporal variability on 96 years is studied by the application of the wavelet transform to five precipitation series at locations in northern California, U.S.A. The wavelet transform spectra are computed for annual total precipitation and wet season precipitation of each record. Comparing two results based on annual and wet season data, all components appear seasonally dependent. Meanwhile, monotonic trends estimated by wavelet transform indicate wetting in the northern California precipitation data. According to the wavelet analysis, the spatial pattern of the precipitation field may have been changed since 1945, and the dominant period is about 16 years. In addition, the recent increasing precipitation trend in northern California can be interpreted as the coupled effect of the extremely long-period component and multi-decadal period components.
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종합적인 가뭄상황판단을 위한 Copulas 기반의 결합가뭄지수의 적용
김상단,류정수,오국열,정상만 한국방재학회 2012 한국방재학회논문집 Vol.12 No.1
가뭄 시작 및 전개 상황에 대한 판단은 여러 가지 가뭄지수들을 이용하고 있는데, 이러한 지수들은 가뭄에 대한 다양한 변수들의 복합적인 영향을 올바르게 반영하고 있지 못한 문제점을 가지고 있다. 이러한 한계를 보완하기 위해, 본 연구에서는copulas를 이용하여 가뭄에 대한 다양한 변수들의 복합적인 영향을 반영하고자 하였다. 1981년부터 2010년까지 전국 60개 지점의 강수 관측 자료로부터 1개월부터 12개월까지 다양한 지속기간을 가진 표준강수지수들 사이에 존재하는 상관구조가 경험적인 copulas를 이용하여 수치적으로 구성된다. 결합가뭄지수(JDI)는 copulas의 분포함수를 사용하는 것으로 정의된다. 제안된JDI를 과거에 발생한 여러 가지 가뭄사상에 적용한 결과, 전반적인 가뭄상황을 판단하는데 효과적으로 적용될 수 있을 것으로기대된다. Current judgment for drought start and development status is based on drought indices which do not capture the jointly correlated effect of various variables related to drought correctly. To address this limitation, we tried to reflect such joint behavior for multiple variables related to drought by using copulas. Utilizing 60 stations of the whole county with 30 years observations(to 2010 from 1981) in Korea, the dependence structures of standardized precipitation indices with various window sizes from 1-to 12-month are constructed from empirical copulas. A joint drought index (JDI) is defined by using the distribution function of copulas. As a result from applying to several historical drought events, the proposed JDI is expected to describe well the overall drought status.
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On the Dependent Structure Between Rainfall Intensity and Duration
김상단 대한토목학회 2004 KSCE JOURNAL OF CIVIL ENGINEERING Vol.8 No.3
In this study, new stochastic point rainfall models which can consider the correlation structure between rainfall intensity and duration are developed. In order to consider the negative and positive correlation simultaneously, the Gumbel's type-II bivariate distribution is applied, and for the cluster structure of rainfall events, the Neyman-Scott cluster point process is selected. In the theoretical point of view, it is shown that the models considering the dependent structure between rainfall intensity and duration have slightly heavier tail autocorrelation functions than the corresponding independent models. Results from generating long time rainfall events show that the dependent models better reproduce historical rainfall time series than the corresponding independent models in the sense of autocorrelation structures, zero rainfall probabilities and extreme rainfall events.
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