Seok-Hwan Hwang

A Comparison of Nonstationary Frequency Analysis Using Successive Average and Moving Average Method

This study employed a nonstationary frequency analysis to consider a trend with successive average and moving average method that are used to derive a relationship between mean of annual maximum rainfall(MAMR) and Gumbel parameters. The Mann-Kendall test is applied to determine the changing trend of the successive and moving average method based MAMR for 62 weather stations. Mann-Kendall test of trend shows an increasing and decreasing trend (p-value

Analysis of Spatial Precipitation Field Using Downscaling on the Korean Peninsula

Precipitation is one of the important factors in the hydrological cycle. It needs to understand accurate of spatial precipitation field because it has large spatio-temporal variability. Precipitation data obtained through the Tropical Rainfall Monitoring Mission (TRMM) 3B43 product is inaccurate because it has 25 km space scale. Downscaling of TRMM 3B43 product can increase the accuracy of spatial precipitation field from 25 km to 1 km scale. The relationship between precipitation and the normalized difference vegetation index(NDVI) (1 km space scale) which is obtained from the Moderate Resolution Imaging Spectroradiometers (MODIS) sensor loaded in Terra satellite is variable at different scales. Therefore regression equations were established and these equations apply to downscaling. Two renormalization strategies, Geographical Difference Analysis (GDA) and Geographical Ratio Analysis (GRA) are implemented for correcting the differences between remote sensing-derived and rain gauge data. As for considering the GDA method results, biases, the root mean-squared error (RMSE), MAE and Index of agreement (IOA) is equal to 4.26 mm, 172.16 mm, 141.95 mm, 0.64 in 2009 and 17.21 mm, 253.43 mm, 310.56 mm, 0.62 in 2011. In this study, we can see the 1km spatial precipitation field map over Korea. It will be possible to get more accurate spatial analysis of the precipitation field through using the additional rain gauges or radar data.

Hydrological Assessment of Multifractal Space-Time Rainfall Downscaling Model: Focusing on Application to the Upstream Watershed of Chungju Dam

In this study, a space-time rainfall grid field generation model based on multifractal theory was verified using nine flood events in the upstream watershed of Chungju dam in South Korea. For this purpose, KMA radar rainfall data sets were analyzed for the space-time multifractal characteristics. Simulated rainfall fields that represent the multifractal characteristics of observed rainfall field were reproduced using the space-time rainfall grid field generation model with log-Poisson distribution and three-dimension wavelet function. Simulated rainfall fields were applied to the S-RAT model as input data and compared with both observed rainfall fields and low-resolution rainfall field runoff. Error analyses using RMSE, RRMSE, MAE, SS, NPE and PTE indicated that the peak discharge increases about 20.03% and the time to peak decreases about 0.81%. keywords : downscaling, multifractal, S-RAT model, space-time rainfall field ..............................................................................................................................................................................................

Flood Runoff Simulation Using S-RAT Model and Radar Rainfall

This study simulated flood runoff of the Gamcheon Basin on the Nakdong River and Ohsipcheon Basin in Samcheok, Gangwon-do, where they frequently recently suffered from flash flood damages. First, consolidating radar rainfall data to consider time and spacial variabilities and development situations is necessary for an analysis of the flash floods. However, radar rainfall data are not reliable enough that it is difficult to use them as measurements of actual ground rainfall. Hence, this paper compared and analyzed the single polarization S-band data of the Gangneung meteorological radar and dual polarization S-band data of the Mt. Biseul radar to grasp their level of contribution to the runoff simulation. Second, a distributed hydrological model is necessary to effectively use GIS information and radar rainfall data of the grid format. Hence, in this paper, we used the S-RAT model as a distributed hydrologic model. The results of this study showed that the accuracy of peak discharge and time when using the distributed hydrologic model and radar rainfall data were similar to the observed values.

A statistical homogeneity analysis of Seoul rainfall using Bootstrap.

In this study, homogeneity analysis was performed between rainfall observation data set of Chukwooki (CWK) and rainfall observation data set of modern rain gage (MRG) using Bootstrap method. Since traditional statistical homogeneity test method are validated only when distribution of their population is known, meteorological data which their statistical distributions of population are complicated were difficult to verify the homogeneity and there were plenty of room for doubt for their statistical significance using historical method. In this reason, in this study homogeneity test was evaluated between two data sets using bootstrap method which is not necessary to infer distribution of population. The test results show that there was an statistical homogeneity between CWK and MRG except for slight impact of climatical trend.