This study has performed the flood risk assessment using PROMETHEE(Preference Ranking Organization METHod for Enrichment Evaluation), one of the multi-criteria decision making methods, for identifying area zones with regional flooding risk in terms of the integrated flood risk management. The 12 representative factors for flood risk assessment are carefully selected and constructed for the three main aspects, such as PF(Pressure Factors), SF(State Factors), and RF(Response Factors) under the P-S-R(Pressure-State-Response) classification system at a spatial resolution of city/county/town units for the Nakdong River Watershed, The entropy weight coefficient method is also applied to calculate the weight of flood risk factors in order to reduce subjective judgement on the effect of weight coefficients. To examine the practical application of the proposed method for identification of flood risk areas, the results with/without the weight coefficients are compared with flooding zones of natural disaster risk areas officially announced in 2010. It is expected that the flood risk assessment method ensured by full verification can establish a rehabilitation priorities of catchments for regional protection plans against flooding disasters with respect to causes and characteristics of past floods.

Studies using drought index to examine return levels of drought can be classified into two approaches: univariate frequency analysis using annual series extracted from drought index time series and multivariate frequency analysis that simultaneously reflects various characteristics of drought. In the case of drought analysis, it is important to properly consider the duration, so, in this study, univariate frequency analysis is performed using the partial duration series. In addition, a bivariate frequency analysis is performed using a relatively simple bivariate exponential distribution to give a more realistic return level to major drought events in the past while reflecting the correlation between drought severities and durations. The drought severity–duration–frequency curves using each of the two frequency analyses are derived, and these curves are used to examine how the drought phenomenon currently in progress is evolving. From this, the advantages and disadvantages of the two approaches, as well as the points to be aware of in application, are discussed. Finally, using the two approaches to the proposed drought frequency analysis, the behavior of Korea’s future extreme droughts is investigated under the conditions of various future climate change scenarios.

No abstract

As extreme floods occur frequently in recent years due to global climate changes, an increase in sudden local flooding of great volume and short duration is becoming the significant danger and loss of life and property in the Korean Peninsula as well as most parts of the world. Since such a local flood rises quite quickly with little or no advance warning to prevent flood damage, this study has developed a new flash flood index for the use in small ungauged catchments. The flash flood index is obtained by relative severity factors estimated in ratios for hydrograph characteristics of each flood event to those of the highest recorded maximum flood. Flood runoff hydrographs for the two selected small ungauged basins are generated from a rainfall-runoff model for the annual maximum rainfall series of long-term observed data. The aim of this study is to present the best-fit regression equation with the high coefficient of determination between the flash flood index and rainfall characteristics to provide the basis database for forecasting a local flood severity directly from rainfall data in small ungauged catchments. The regression results in this study show that the proposed flash flood index has a very high relation to a certain rainfall pattern for both study basins. It is therefore expected that the regression equations between the new flash flood index and rainfall characteristics can provide better understanding of the hydrologic behavior of local flash flooding using rainfall patterns in small ungauged catchments.

For a period of 5 years beginning in May, 2011, the Ministry of Public Safety and Security has, by way of the "Development and Construction of a Flood Forecasting and Warning System for Medium and Small Streams" research project, undertaken research related to medium and small stream flood warning mentioned above as well as the creation of a flood forecasting and warning system. As a part of the project, this study has proposed the criteria for the issuance of medium and small stream flood warnings in urban areas, targeting the Jeongneung stream located in Dongdaemun-gu, Seoul. In order to establish flood warning issuance criteria, analysis was undertaken applying the "Flood Forecasting Estimation Methodology of Standard Rainfall for Urban Mid and Small Rivers considering Upper-and Down-stream Water Levels" scenario put forward by Song et al. (2014) in the case of complex warning criteria estimation methods in line with rising water levels. During the course of research, the HEC-HMS model was applied to the relationship between rainfall-outflow, while analysis of the outflow-water level relationship calculated the standard precipitation amount for the issuance of flood warning in accordance with drainage conditions by constructing the Jeongneung stream basin based on HEC-RAS. The results of calculations took into account the feasibility of criteria for the issuance of flood forecasting and warnings for streams in urban areas through a comparison of real-time water level observations in Jeongneung stream.