• Journal of Korea Water Resources Association
• /
• v.49 no.1
• /
• pp.41-49
• /
• 2016

This study proposed a new drought index considering the accumulative pattern of daily rainfall, i.e., Rainfall Accumulation Drought Index (RADI). The RADI can be easily calculated at daily scale by comparing the long-term averaged cumulative rainfall to the observed cumulative rainfall for a specific duration. This study evaluated the availability of the RADI in the field of monitoring short-term and long-term droughts by investigating the spatial and temporal variability and the recurrence cycle of drought in South Korea. To present the short-term and long-term droughts, the various SPIs with different durations should be used in practice. However, the RADI can present and monitor both short-term and long-term droughts as a single index. By investigating the national average of the RADI, specific drought patterns of 20-year cycle were identified in this study. This study also proposed a five-level drought classification considering occurrence probability that would be a suitable alternative as a drought criterion for drought forecast/response.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.9 no.1
• /
• pp.135-144
• /
• 2009

The objective of this study is to examine the effect of hydrological factors on critical durations, and to analyze the relationship between the watershed characteristics and the critical duration of design rainfall in the medium sized catchments. Hydrological factors are used to return period, probable intensity formula, hydrograph method, effective rainfall and temporal pattern of design rainfall. Hydrologic analysis has done over the 44 medium sized catchments with $50{\sim}5,000{\beta}{\yen}$. Watershed characteristics such as catchment area, channel length, channel slope, catchment slope, time to peak, concentration of time and curve number were used to simulate correlation analysis. All of hydrological factors except return period influence to the critical duration of design rainfall. Also, it is revealed that critical duration is influenced by the watershed characteristics such as area, channel length, channel slope and catchment slope. Multiple regression analysis using watershed characteristics is carried out for the estimation of relationship among these. And the 7 type equations are proposed by the multiple regression using watershed characteristics and critical duration of design rainfall. The determination coefficient of multiple regression equations shows $0.96{\sim}0.97$.

• Journal of Korea Water Resources Association
• /
• v.45 no.3
• /
• pp.275-290
• /
• 2012

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.

• Water for future
• /
• v.20 no.2
• /
• pp.139-150
• /
• 1987

The present study is to develop the hydrologic analysis procedure for the purpose of drawing the probable isohyetal charts in Korea. In the establishment of optimal distribution types, the eleven continuous probability distribution types included the transformed variable normal distribution (Y-k method) is applied to the annual maximum rainfall depth series in each duration. The optimal selection of distribution is done by Chi-square test and Kolmogorov-Smirnov test in the eui-class interval. The application of probability distribution is checked by the fitting on four durations of annual maximum rainfall data(10 min., 60 min., 6 hrs., and 24hrs.) at four meteorological stations in Korea (Seoul, In Cheon, Bu san, and Kwang Ju). The properties in hydrologic application of the considered distribution and the hydrologic characteristics of the applied rainfall data groups are investigated from the results of this study.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.5 no.2 s.17
• /
• pp.17-28
• /
• 2005

The objective of this study is to evaluate the critical duration between detention facility and flood control facility of small size catchment. 4 small size catchments are applied for hydrological analysis and rainfall excess is computed by using the NRCS Runoff Curve Number method. The critical duration of detention facility and flood control facility is evaluated using the concept of allowable release rate. The conclusions studied in this study are as follows; (1) The type of temporal pattern of design rainfall which causes maximum storage ratio has resulted in Huff's 2 quartile in case of the use of the concept of allowable release rate. (2) Based on (1) of conclusion, the critical durations of flood control facility are similar to those of detention facility, which is used for uncontrolled single detention pond.

• Journal of Korea Water Resources Association
• /
• v.43 no.1
• /
• pp.15-24
• /
• 2010

Regional frequency analysis is often used to overcome the limitation of point frequency analysis to estimate probability rainfall depths. However, point frequency analysis is still used in drought analyses. This study proposed a practical method to categorize the homogeneous regions of drought characteristics for the analyses of regional characteristics of droughts in Korea. Using rainfall data from 58 observation stations managed by the Korea Meteorological Administration, this study calculated drought attributes, i.e., mean drought indices for various durations using the Standardized Precipitation Index (SPI) and drought severities expressed by durations, depth, and intensity. The drought attributes provided useful information for categorizing stations into the hydrological homogeneous regions. This study introduced a cluster analysis with K-means techniques to group observation stations. The cluster analysis grouped observation stations into 6 regions in Korea. The data in the hydrological homogeneous region would be used in spatial analysis of drought characteristics and drought regional frequency analysis.

• Water for future
• /
• v.28 no.5
• /
• pp.205-217
• /
• 1995

The historical data from 3, 550 event storms during 11 years in Wi-stream basin have been used to investigate the statistical parameter of the time distribution for design storms by the method of Yen-Chow, Huff, Pilgrim-Cordery and Mononobe. The dimensionless value of triangular hyetograph, $a^0$, ranges from 0.44 to 0.50 and trapezoidal hyetograph, $h^0$, value increases as the duration time is getting longer in Yen-Chow method. In the Huff, the second-quartile storms occurred most frequently and third-quartile storms occurred most infrequently. In the Pilgrim-Cordery, the shapes for shorter than 6-hour durations are advanced tendency. However, for longer than 6-hour durations show delayed tendency. In the Mononobe, every one hour rainfall occured Centered Type. The application of these methods for each duration time was tested by using the observed rainfall-runoff data of Wi-stream basin. As a result, the reappearance of hydrographs of triangular hyetograph by Yen-Chow method showed promising, and it was approved to be used for prediction of the ungaged basins.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.44 no.2
• /
• pp.161-172
• /
• 2024

A Copula approach has the advantage of providing structural dependencies for representing multivariate distributions for the hydrometeorological variable marginal distribution involved, however, copulas are inflexible for extending in high dimensions, and satisfy certain assumptions to make the dependency. In addition, since the process of estimating design rainfall under the future climate associated with durations given a return period is mainly analyzed by 24-hour annual maximum rainfalls, the dependency structure contains information only on the daily and sub-daily extreme precipitation. Methods based on bivariate copula do not provide information for other duration's dependencies, which causes the intensity to be reversed. The vine copula has been proposed to process the multivariate analysis as vines consisting of trees with nodes and edges connecting pair-copula construction. In this study, we aimed to downscale under climate change to produce sub-daily extreme precipitation data considering different durations based on vine copula.

• Journal of Korea Water Resources Association
• /
• v.56 no.4
• /
• pp.261-272
• /
• 2023

In recent years, natural disasters such as heavy rainfall and typhoons have occurred more frequently, and their severity has increased due to climate change. The Korea Meteorological Administration (KMA) currently uses the same criteria for all regions in Korea for watch and warning based on the maximum cumulative rainfall with durations of 3-hour and 12-hour to reduce damage. However, KMA's criteria do not consider the regional characteristics of damages caused by heavy rainfall and typhoon events. In this regard, it is necessary to develop new criteria considering regional characteristics of damage and cumulative rainfalls in durations, establishing four stages: blue, yellow, orange, and red. A classification model, called DSCM (Disaster Severity Classification Model), for the four-stage disaster severity was developed using four machine learning models (Decision Tree, Support Vector Machine, Random Forest, and XGBoost). This study applied DSCM to local governments of Seoul, Incheon, and Gyeonggi Province province. To develop DSCM, we used data on rainfall, cumulative rainfall, maximum rainfalls for durations of 3-hour and 12-hour, and antecedent rainfall as independent variables, and a 4-class damage scale for heavy rain damage and typhoon damage for each local government as dependent variables. As a result, the Decision Tree model had the highest accuracy with an F1-Score of 0.56. We believe that this developed DSCM can help identify disaster risk at each stage and contribute to reducing damage through efficient disaster management for local governments based on specific events.

• Journal of Korea Water Resources Association
• /
• v.31 no.3
• /
• pp.253-267
• /
• 1998

In this study, ILLUDAS and SWMM were applied for Dongsucheon basin, Incheon and Test basin, Cheongju. The main parameters (II, IA, IS, SI, SR, SS) which are included in those of each model depending on runoff results were determined, and sensitivity ratios were estimated in order to evaluate and compare the characteristics of each modEL. Total runoff ratio for almost parameters turned out to have a linear relation to the rainfall durations and the scale of basin area but have nothing to do with rainfall distributions. Sensitivity ratios turned out to have a linear relation for the infiltration and soil parameters of ILLUDAS as well as all parameters of SWMM. ronoff sensitivity ratios for almost parameters were smaller than 1.0 because the impacts of total runoff were bigger than those of peak runoff. And runoff sensitivity ratio was equal to 1.0 for the roughness coefficient of SWMM. Total runoff ratio, peak runoff ratio and runoff sensitivity ratio for the selected parameters of those models were presented asthe tables and figures according to the scale of basin area, rainfall durations such as 60, 120, and 180 minutes and Huff's 4th quartiles rainfall distributions. Keywords : ILLUDAS, SWMM, parameter, sensitivity analysis, sensitivity ratio.