Jungsoo Yoon

Assessment of Rainfall Simulated on RCP Scenarios for Disaster Management

This study assessed the daily rainfall simulated on RCP(Representative Concentration Pathway) scenarios for disaster management. First, in the result that compared characteristic of the simulated daily rainfall with characteristic of the observed daily rainfall, annual rainfall and annual maximum daily rainfall estimated from the simulated daily rainfall was similar to those estimated from the observed daily rainfall. But monthly rainfall and rainy days of the simulated daily rainfall did not reflect the characteristic of the observed daily rainfall. And in the result that compared the simulated rainfall with the observed rainfall during 2000 yr~2011 yr, annual maximum daily rainfall and rainy days of the simulated rainfall was different from those of the observed rainfall. Finally, the simulated rainfall had smaller probability rainfall than the observed rainfall in certain rainfall point.

Quantification of Flood Runoff Reduction Effect of Storage Facilities by the Decrease in CN

AbstractThis study proposed a methodology for quantifying the flood runoff reduction effect of storage facilities by curve number (CN). The runoff hydrographs for various rainfall durations and return periods were derived using the modified rational method. The effect of runoff reduction due to the introduction of storage facilities was then quantified by CN. The result derived was summarized in a graph showing the decrease in CN as an effect of the runoff reduction with respect to the rainfall duration, return period, runoff coefficient of the catchment, and size of the storage facility. The runoff reduction effect of a storage facility was able to be easily and directly estimated using the derived graph. The result derived was also found to be well matched with the previous study for three different sites.

Evaluation of Spatially Disproportionate Rain Gauge Network for the Correction of Mean-Field Bias of Radar Rainfall: A Case Study of Ganghwa Rain Radar

Estimation of the mean-field bias of radar rainfall is to determine the difference between the areal means of radar and rain gauge rainfall, where the rain gauge rainfall is assumed to be the truth. To exactly determine this bias, the variance of the difference between two observations must be small enough, thus, enough number of observations is indispensible. So, the problem becomes to determine the number of rain gauges to satisfy the level of variance of the difference between two observations. Especially, this study focuses on the case when the rain gauges are disproportionate spatially. This is the problem for the Ganghwa rain radar for the observation of rainfall within the Imjin river basin and the same problem also occurs when a radar is located in between land and ocean. This study considered the Imjin river basin, and compared two cases when rain gauges are available only within the downstream part, about one third of the whole basin, and over the whole basin. Based on the results derived, the rain gauge density within the downstream part of the Imjin river basin was proposed to secure the same accuracy obtained when the rain gauges are available over the whole Imjin river basin.

Application of an empirical method to improve radar rainfall estimation using cross governmental dual-pol. radars

Three leading agencies under different ministries Korea Meteorological Administration (KMA) in the ministry of Environment, Han river control office in the Ministry of Land, Infrastructure and Transport (MOLIT) and Weather Group of ROK Air Force in the Ministry of National Defense (MND) have been operated radars in the purpose of observing weather, hydrology and military operational weather in Korea. Eight S-band dual-pol. radars have been newly installed or replaced by these ministries over different places by 2015. However each ministry has different aims of operating radars, observation strategies, data processing algorithms, etc. Due to the differences, there is a wide level of accuracy on observed radar data as well as the composite images made of the cross governmental radar measurement. Gaining fairly high level of accuracy on radar data obtained by different agencies has been shared as a great concern by the ministries. Thus, “an agreement of harmonizing weather and hydrological radar products” was made by the three ministries in 2010. Particularly, this is very important to produce better rainfall estimation using the cross governmental radar measurement. Weather Radar Center(WRC) in KMA has been developed an empirical method using measurements observed by Yongin testbed radar. This study is aiming to examine the efficiency of the empirical method to improve the accuracies of radar rainfalls estimated from cross governmental dual-pol. radar measurements. As a result, the radar rainfalls of three radars (Baengnyeongdo, Biseulsan, and, Sobaeksan Radar) were shown improvement in accuracy (1-NE) up to 70% using data from May to October in 2015. Also, the range of the accuracies in radar rainfall estimation, which were from 30% to 60% before adjusting polarimetric variables, were decreased from 65% to 70% after adjusting polarimetric variables.

Evaluation of Error Indices of Radar Rain Rate Targeting Rainfall-Runoff Analysis

AbstractThis study evaluates several error indices of the radar rain rate from the viewpoint of the accuracy of rainfall-runoff analysis. The error indices considered in this study are the mean error (ME), mean absolute error (MAE), normalized standard deviation (NSD), correlation coefficient (CC), bias (BS), and radar rain rate quality criterion (RRQC). These indices were analyzed using the concept of sum of squares (SS) and mean squares (MS) in the analysis of variance (ANOVA), which explains how the bias and random error of the radar rain rate are combined in an error index. Also, these error indices were linked to the errors in the runoff result, such as the total runoff volume, peak flow, and peak time. As an application, two dam basins in Korea were selected, the Chungju Dam basin and the Namgang Dam basin. The radar rain rates from Gwangdeoksan Radar and Gudeoksan Radar were used as input for the rainfall-runoff analysis. Six different rainfall events were applied to secure various rainfall types. ...

On the Use of Threshold for the Ground Validation of Satellite Rain Rate

Ground-truthing is a major problem in the satellite estimation of rain rate. This problem is that the measurement taken by the satellite sensor is fundamentally different from the one it is compared with on the ground. Additionally, since the satellite has the limited capability to measure the light rain rate exactly, the comparison should also consider the threshold value of satellite rain rate. This paper proposes a ground-truth design with threshold for the satellite rain rate. This ground-truth design is the generalization of the conventional ground-truth design which considered the only (zero, nonzero) and (nonzero, nonzero) measurement pairs. The mean-square error is used as an index of accuracy in estimating the ground measurement by satellite measurement. An application to the artificial random field shows that the proposed ground-truth design with threshold is valid as the design bias is zero. The same result is also derived in the application to the COMS (Communication, Ocean, and Meteorological Satellite) rain rate data in Korea.