• Water Engineering Research
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• v.3 no.1
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• pp.31-44
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• 2002

The effect of diurnal cycle, intermittent visit of observation satellite, sensor installation, partial coverage of remote sensing, heterogeneity of soil properties and precipitation to the soil moisture estimation error were analyzed to present the global sampling strategy of soil moisture. Three models, the theoretical soil moisture model, WGR model proposed Waymire of at. (1984) to generate rainfall, and Turning Band Method to generate two dimensional soil porosity, active soil depth and loss coefficient field were used to construct sufficient two-dimensional soil moisture data based on different scenarios. The sampling error is dominated by sampling interval and design scheme. The effect of heterogeneity of soil properties and rainfall to sampling error is smaller than that of temporal gap and spatial gap. Selecting a small sampling interval can dramatically reduce the sampling error generated by other factors such as heterogeneity of rainfall, soil properties, topography, and climatic conditions. If the annual mean of coverage portion is about 90%, the effect of partial coverage to sampling error can be disregarded. The water retention capacity of fields is very important in the sampling error. The smaller the water retention capacity of the field (small soil porosity and thin active soil depth), the greater the sampling error. These results indicate that the sampling error is very sensitive to water retention capacity. Block random installation gets more accurate data than random installation of soil moisture gages. The Walnut Gulch soil moisture data show that the diurnal variation of soil moisture causes sampling error between 1 and 4 % in daily estimation.

• Journal of Korea Water Resources Association
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• v.37 no.9
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• pp.759-769
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• 2004

This study proposes a new methodology to derive the areal reduction factor (ARF) using mixed probability density functions. Estimation of ARFs requires using the simultaneous rainfall data over the basin, which is rarely available in general. The new methodology Proposed in this study uses more available daily rainfall data during a given period, so the mixed probability density functions should be introduced to explain both the rainfall intermittency and variability. This study applied the mixed gamma distribution for the derivation of ARFs for the Keum river basin, and found that the new method is easier for application as well as it provides very comparable results.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.2
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• pp.67-74
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• 2002

The purpose of this study was to investigate the effects of ponding depth treatment on water balance in paddy fields. Three ponding depth treatments, very shallow, shallow, and deep were used. The experimental plots were three 80m $\times$ 8m rectangular plots. Daily values of rainfall amount, ponding depth, irrigation water, drainage water, evapotranspiration, and infiltration were measured in the field. The ponding depth was continuously observed by water level logger during the growing season. The ET was measured by 1-m diameter PVC lysimeters. Irrigation water volume was measured by 75 mm pipe flowmeters and the drainage water volume by 75 mm pipe flowmeters and a recording Parshall flume. The results showed that irrigation water depths were 688.9 mm, 513.6 mm, and 624.4 mm in very shallow, shallow, and deep ponding, respectively. The effective rainfall amounts (effective ratio) were 243.7 mm(48.8%), 344.6 mm(68.9%), and 272.9 mm(54.6%) in very shallow, shallow, and deep ponding, respectively. The three treatments did not show any statistical difference in growth and yields. But the shallow depth treatment showed the largest yield.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.126-126
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• 2022

Climate change has continued to impact meteorological factors like rainfall in many countries including Nigeria. Thus, altering the rainfall patterns which subsequently affect the crop yield. Maize is an important cereal grown in northern Nigeria, along with sorghum, rice, and millet. Due to the challenge of water scarcity during the dry season, it has become critical to design appropriate strategies for planning, developing, and management of the limited available water resources to increase the maize yield. This study, therefore, determines the quantity of water required to produce maize from planting to harvesting and the impact of drought on maize during different growth stages in the region. Rainfall data from six rain gauge stations for a period of 36 years (1979-2014) was considered for the analysis. The standardized precipitation and evapotranspiration index (SPEI) is used to evaluate the severity of drought. Using the CROPWAT model, the evapotranspiration was calculated using the Penman-Monteith method, while the crop water requirements (CWRs) and irrigation scheduling for the maize crop was also determined. Irrigation was considered for 100% of critical soil moisture loss. At different phases of maize crop growth, the model predicted daily and monthly crop water requirements. The crop water requirement was found to be 319.0 mm and the irrigation requirement was 15.5 mm. The CROPWAT 8.0 model adequately estimated the yield reduction caused by water stress and climatic impacts, which makes this model appropriate for determining the crop water requirements, irrigation planning, and management.

• Magazine of the Korean Society of Agricultural Engineers
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• v.42 no.1
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• pp.57-65
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• 2000

The objective of this paper are to present a realistic methodology to estimate the daily water supply rates form irrigation pumping stattions, to validate it with the field data, and to report the daily irrigation pumping rates from the Han river basin. Five-year historical pumping records were collected from seventy-three pumping stations in the Han river basin. And the daily pumping rates were estimated from the electrical consumption records. The pumping patterns from the stations were analyzed and the results were applied to ungauged pumping stations in the basin. The method was appliedto five stations which were field monitored during the irragation periods in 1998. The relative errors between the observed and simulated water pumpage ranged from 1.4 to 7.0 percent. This indicates that the proposed method is valid to apply for estimating the pumping rates for agricultural lands. During 1993 to 1997, the annual average water pumpaging from the Han river and the tributaries were 350 million cubic meter. The annual water supply from the pumping stations varied from 973 to 1.377 mm in depth and the mean was 1,170 mm. The major factor affecting the annual variations was attributed to the rainfall during the growing seasons.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.6
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• pp.45-53
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• 2014

This study presents a system dynamics modeling approach to simulate daily streamflow in a watershed including wastewater treatment plant which contributes to irrigation water supply. The conceptual system dynamics model considering the complex and dynamic hydrological processes in the watershed was developed. The model was calibrated and validated each for two years based on observed flow data. Model performances in terms of $E_{NS}$, RSR, PBIAS, and $R^2$ were 0.64, 0.60, -3.6 %, and 0.64 for calibration period, and 0.66, 0.58, -2.6 %, and 0.66 for validation period, respectively, showing an applicability on generating the daily streamflow. System dynamics modeling approach could help better understand the hydrological behavior of the watershed being reused wastewater for agriculture, by providing graphical dynamics of the hydrological processes as well as conventional rainfall-runoff model results.

• Atmosphere
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• v.28 no.3
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• pp.273-289
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• 2018

This paper evaluates daily precipitation products from Integrated Multisatellite Retrievals for Global Precipitation Measurement (IMERG), Tropical Rainfall Measuring Mission Multisatellite (TRMM) Precipitation Analysis (TMPA), and the Climate Prediction Center Morphing Method (CMORPH), validated against gauge observation over South Korea and gauge-based analysis data East Asia during one year from June 2014 to May 2015. It is found that the three products effectively capture the seasonal variation of mean precipitation with relatively good correlation from spring to fall. Among them, IMERG and TMPA show quite similar precipitation characteristics but overall underestimation is found from all precipitation products during winter compared with observation. IMERG shows reliably high performance in precipitation for all seasons, showing the most unbiased and accurate precipitation estimation. However, it is also noticed that IMERG reveals overestimated precipitation for heavier precipitation thresholds. This assessment work suggests the validity of the IMERG product for not only seasonal precipitation but also daily precipitation, which has the potential to be used as reference precipitation data.

• Korean Journal of Hydrosciences
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• v.4
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• pp.1-9
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• 1993

It is a major objective for the management and operation of water resources system to forecast streamflows. The applicability of artificial neural network model to hydrologic system is analyzed and the performance is compared by statistical method with observed. Multi-layered perception was used to model rainfall-runoff process at Pyung Chang River Basin in Korea. The neural network model has the function of learning the process which can be trained with the error backpropagation (EBP) algorithm in two phases; (1) learning phase permits to find the best parameters(weight matrix) between input and output. (2) adaptive phase use the EBP algorithm in order to learn from the provided data. The generalization results have been obtained on forecasting the daily and hourly streamflows by assuming them with the structure of ARMA model. The results show validities in applying to hydrologic forecasting system.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1870-1875
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• 2006

This study was carried out to investigate the applicability of SAC-SMA model with parameters which were derived from analytical relationships proposed by Koren etc. (2000), with various data of soil properties in a basin. The studied basin is Yongdam dam basin and the daily runoff with 2003-year hydrological data was simulated. Simulated runoff results were compared with those measured at three check points(Chuchun, Donhyang and Yongdam) and analyzed through the statistical techniques such as VE(Volume Error), RMSE(Root Mean Squared Error) and CORR(Correlation). As a result of analyses, the good agreement was obtained between simulated and measured results.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1389-1392
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• 2009

본 연구에서는 기상청에서 관측하고 있는 서울지점을 대상으로 일강우자료를 활용하여 강우사상의 변화 특성에 대한 변동성과 경향성 분석을 수행하였다. 분석대상자료는 서울지점에서 관측된 일강우자료를 1958년부터 2007년까지 50년간 자료를 이용하였다. 일강우자료를 이용하여 연강우량, 계절별강우량 및 월별강우량을 추출하였다. 또한, 각 연, 계절 및 월별로 일강우량이 지속기간별로 1, 2, 3, 4, 5, 7일 최대강우량과 일강우량이 발생한 강우깊이가 분석대상기간에 따라 0, 10, 30, 50, 70, 80, 90, 95, 99% 이상 발생한 강우일수에 대한 분석을 수행하였다. 분석 결과에서 평균과 표준편차의 변동성은 일부 자료에서 확인되고 있으며 경향성은 거의 없는 것으로 나타났다. 그러므로 강우사상의 특성의 평균과 표준편차가 변화하고 있으므로 이에 대한 심도 있는 연구가 필요하다.