• Magazine of the Korean Society of Agricultural Engineers
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• v.23 no.2
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• pp.45-53
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• 1981

Long term precipitation gaging station record (58 years) was analyzed by progressive mean method to compare the estimated effective period of records for computing mean and probable values. Obtained results are as follows: 1. Fifty-eight years precipitation records at Jinju, Gyeong Sang Nam Do was analyzed by double mass analysis method. Result was appeared that the record was consistent with time. 2. The effective period of records for estimating mean values with the departure of 5% or less from the true mean are up to 33 years for annual precipitation, 20 years for annual maximum daily precipitation and 45 years for maximum successive dry days in summer season. 3. To estimate the probable values by Gumbel-Chow method within the departure of 5% level from true value, periods of 51 years, 38 years and 45 years were required for annual precipitation, annual maximum daily precipitation and maximum successive dry days in summer season, respectively.

• Journal of Korean Society of Water and Wastewater
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• v.10 no.2
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• pp.88-103
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• 1996

The objective of this study is to develop stochastic and deterministic models which could be used to synthesize water application time series. Adaptive models using mulitivariate ARIMA(Transfer Function Model) are developed for daily urban water use forecasting. The model considers several variables on which water demands is dependent. The dynamic response of water demands to several factors(e.g. weekday, average temperature, minimum temperature, maximum temperature, humidity, cloudiness, rainfall) are characterized in the model by transfer functions. Daily water use data of Kumi city in 1992 are employed for model parameter estimation. Meteorological data of Seonsan station are utilized to input variables because Kumi has no records about the meteorological factor data.To determine the main factors influencing water use, autocorrelogram and cross correlogram analysis are performed. Through the identification, parameter estimation, and diagnostic checking of tentative model, final transfer function models by each month are established. The simulation output by transfer function models are compared to a historical data and shows the good agreement.

• Journal of Korean Society for Atmospheric Environment
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• v.30 no.2
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• pp.128-138
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• 2014

This study has analyzed the concentration variation of four air pollutants ($PM_{10}$, $NO_2$, CO, and $SO_2$) during the typhoon periods over 10 years (2002~2011). In this study, 10 typhoon events which had rainfalls in Korean Peninsula were selected during the study period. The analysis was performed using the observation data of both the air pollutants and rainfall. In order to examine and compare the concentrations of the air pollutants between normal periods and typhoon periods, we have obtained monthly average concentrations from July to September and daily average concentrations during typhoon periods. For the period from July to September, 34% of the total rainfalls can be explained by typhoons, and the concentration of air pollutants during the typhoon period was lower than the normal period. In addition, the concentration variations of the pollutants during the typhoon period were analyzed according to two categories: differences in the concentrations between the day before and the day of the typhoon (Case 1) and between the day before and after the typhoon (Case 2). The results indicated that the reduction rate of $PM_{10}$, $NO_2$, CO, and $SO_2$ was 30.1%, 17.9%, 11.6%, 9.7% (Case 1) and 22.8%, 21.0%, 9.0%, 8.0% (Case 2), respectively. This result suggested that air quality was significantly improved during the typhoon period than after the typhoon period by the rainfall.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.1
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• pp.29-39
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• 2018

In this study, the applicabilities of flood risk indices using FVI from IPCC, PSR method from OECD, and DPSIR method from EEA, were analyzed. Normalized values of daily maximum rainfall, hourly maximum rainfall, ten minute maximum rainfall, annual precipitation, total days of heavy rainfall (more than 80mm/day), density of population, density of asset, DEM, road statistics, river maintenance ratio, reservoir capacity, supply ratio of water supply and sewerage, and pumping capacity were constructed from 2000 to 2015 for nationwide 113 watersheds, to estimate flood risk indices. The estimated indices were compared to 4 different types of flood damage such as the number of casualties, damage area, the amount of flood damage, and flood frequency. The relationships between flood indices and different flood damage types demonstrated that the flood index using the PSR method shows better results for the amount of flood damage, the number of casualties and damage area, and the flood index using the DPSIR method shows better results for flood frequency.

• Journal of Korean Society on Water Environment
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• v.33 no.5
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• pp.531-537
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• 2017

The biologic Oxygen Demand (BOD) is a reliable and generally accepted indicator of water pollution by organic pollutants. Accordingly, estimation of BOD export from paddies carries important implications fwith regard to water management in rural areas. In this study, hydrology and BOD concentration were monitored during the period 2008 through 2012, in an effort to understand the characteristics of BOD export from paddy fields. The findings demonstrated that BOD load by rainfall above 50 mm. occupied about 50 % of total load, whereas the load by less than ten mm. rainfall occupied about 29 % of the total load during periods of stormy activity. It therefore seems that it could be possible to reduce the BOD load up to 29 % during storm periods, when drainage control conducted for rainfall less than ten mm.(an amount which is relatively easy to manage). The documented mean loads of storm and non-storm were $17.1kg\;ha^{-1}\;yr^{-1}$ and $11.2kg\;ha^{-1}\;yr^{-1}$, respectively. The BOD load during the significant rainfall period was similar to the renewed unit load by NIER (2014). However, there were substantial differences between unit load and actual load when the non-storm load was incorporated into the BOD load estimation from paddy fields. In view of the foregoing, it is felt that, the non-storm load needs to be further considered and managed for the successful implementation of Total Maximum Daily Load (TMDL) program.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.5
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• pp.89-99
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• 2014

The goal of this study was to evaluate sediment reduction effects of VFS (vegetative filter strip) applied for Iksan area in Saemangeum watershed. This study simulated runoff and sediment load from different types of uplands using VFSMOD-W. The general upland characteristics of the study area was investigated to build reasonable scenarios of the simulation. The simulation scenarios were designed by various areas, shapes, and slopes of uplands. Grass mixture was selected as VFS vegetation and the size of VFS was fixed as 10 % of uplands area. Additionally 50mm, 100mm, 150mm of daily rainfall were applied for the runoff and sediment simulation. As results, the calculated runoff and sediment loads were obtained $20.7{\sim}1,030.6m^3$ and 568.4~675,731.4 kg for the range of 0.1~1.0 ha of uplands with 7 % and 15 % slopes. The reduction effects on runoff and sediment were obtained 5~10 % and 21.0~47.7 % respectively from VFS applications. The VFSMOD-W simulations showed that runoff tended to increase as upland area and amount of rainfall increased while sediment increased when slope, length and area of uplands and amount of rainfall increased. These results indicated that rainfall amount and upland size are the critical factors for the generation of runoff and sediment load. In order to support this conclusion, further studies such as, long term monitoring, field experiments, and to calibrate and evaluate the model are necessary.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.1
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• pp.71-79
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• 2017

Climate change phenomenon is posing a serious threat to sustainable corn production in Ghana. This study investigated the impacts of climate change on the rain-fed corn yield in the Dangme East district, Ghana by using Aquacrop model with a daily weather data set of 22-year from 1992 to 2013. Analysis of the weather data showed that the area is facing a warming trend as the numbers of years hotter and drier than the normal seemed to be increasing. Aquacrop model was assessed using the limited observed data to verify model's sufficiency, and showed credible results of $R^2$ and Nash-Sutcliffe efficiency (NSE). In order to simulate the corn yield response to climate variability four climate change scenarios were designed by varying long-term average temperature in the range of ${\pm}1^{\circ}C{\sim}{\pm}3^{\circ}C$ and average annual rainfall to ${\pm}5%{\sim}{\pm}30%$, respectively. Generally, the corn yield was negatively correlated to temperature rise and rainfall reduction. Rainfall variations showed more prominent impacts on the corn yield than that of temperature variations. The reduction in average rainfall would instantly limit the crop growth rate and the corn yield irrespective of the temperature variations.

• Korean Journal of Soil Science and Fertilizer
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• v.48 no.4
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• pp.246-254
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• 2015

This study explored the effect of rainfall pattern and soil characteristics on water management in rice paddy fields, using a soil water balance model, BUDGET. In two sites with different soil textural group, coarse loamy soil (Gangseo series) and fine soil (Hwadong series), respectively, we have monitored daily decrease of water depth, percolation rate, and groundwater table. The observed evapotranspiration (ET) was obtained from differences between water depth decrease and percolation rate. The root mean square difference values between observed and BUDGET-estimated ET ranged between 10% and 20% of the average observed ET. This is comparable to the measurement uncertainty, suggesting that the BUDGET model can provide reliable ET estimation for rice fields. In BUDGET model of this study, irrigation requirement was determined as minimum water need for maintaining water-saturated soil surface, assuming 100 mm of bund height and no lateral loss of water. The model results showed different water balance and irrigation requirement with the different soil profile and indicated that minimum percolation rate by plow pan could determine the irrigation requirement of rice paddy field. For the condition of different rainfall distribution, the results presented different irrigation period and amounts, representing the importance of securing water for irrigation against different rainfall pattern.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.6
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• pp.983-990
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• 2011

Universal Soil Loss Equation (USLE) has been used to estimate potential long-term soil erosion in the fields. However, the USLE does not estimate sediment yield due to lack of module considering sediment delivery ratio (SDR) for watershed application. For that reason, the Sediment Assessment Tool for Effective Erosion Control (SATEEC) system was developed and applied to compute the sediment yield at watershed scale. However, the R factor of current SATEEC Ver. 2.1 was estimated based on 5-day antecedent rainfall, it is not related with fundamental concept of R factor. To compute R factor accurately, the energy of rainfall strikes should be considered. In this study, the R module in the SATEEC system was enhanced using formulas of Williams, Foster, Cooley, CREAMS which could consider the energy of rainfall strikes. The enhanced SATEEC system ver. 2.2 was applied to the Imha watershed and monthly sediment yield was estimated. As a result of this study, the $R^2$ and NSE values are 0.591 and 0.573 for calibration period, and 0.927 and 0.911 for validation period, respectively. The results demonstrate the enhanced SATEEC System estimates the sediment yield suitably, and it could be used to establish the detailed environmental policy standard using USLE input dataset at watershed scale.

• Journal of Climate Change Research
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• v.7 no.4
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• pp.397-405
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• 2016

For better understand of the soil respiration characteristic in ecosystem, it is necessary to accurately determine the daily, monthly and seasonal $CO_2$ flux related to various environmental factors. In general, soil respiration is being measured on a sunny day. But soil respiration is known to be affected by soil temperature and soil moisture content. In case of forestry, changes in soil moisture content are entirely dependent on rainfall. If we calculated the monthly soil respiration measured based on sunny days data only, it could be a factor that loses credibility soil respiration. On this study, we measured soil respiration on Pinus koraiensis plantation at Mt. Taehwa of Gwangju, Gyeonggi-do on sunny and rainy days in 2012, using Automatic Open-Closed Chamber system (AOCC) and portable $CO_2$ analyzer (GMP343). Then we computed the regression equations using sunny days data, precipitation less than 10 mm data, and precipitation over 10 mm data. At first, there were no significant differences in observed data and computed data. But less than 10 mm precipitation, computed data was 26.5% lower than observed data. Precipitation over 10 mm, on the other hand, the former was 29.3% higher than the latter. In each case, it showed significant differences between observed and computed data (p<0.05). So if we computed regression equation using soil respiration measured sunny days only, about 30% of annual soil respiration could be overestimated. Through further study, we suggest the subdivision and computation of regression equation on the basis of the rainfall intensity.