• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.389-389
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• 2021

불투수면의 증가는 유량변화 및 지하수위와 기저유출의 감소로 이어질 수 있으며 기저유량의 감소는 건기 시 하천의 유량공급까지 영향을 줄 수 있다. 이런 이유로 기저유량에 대한 정확한 분석 및 검증은 반드시 필요하지만 지표수-지하수를 고려한 통합적 해석의 어려움과 기저유출 분석에 대한 불확실성 및 기술적 한계로 분석이 어려운 실정이다. 따라서 본 연구에서는 SWAT 해석을 통해 획득한 모의유량과 관측유량을 비교하여 R²값을 계산하였으며 SWAT-CUP을 이용하여 검보정을 실시한 후 기저유출량을 정량적으로 산정하고 비교하였다. 연구지역 모의기간은 실측 유량자료가 있는 4개년을 대상으로 모의 하였으며 SWAT-CUP을 이용한 검보정 시 모의 횟수는 연구자에 따라 다양한 기준을 제시하고 있지만 모의 시간 대비 최대 효율인 1,000회 수행하였다. 또한 관측유량에 대하여 SPE(Swat Parameter Estimator) 알고리즘으로 모의유량을 최적화하였다. 실측유량과 모의유량을 비교한 결과 SWAT 분석에 의한 R²값보다 SWAT-CUP을 이용하여 검보정을 수행한 R²값이 높게 나타나 검보정 효과를 확인하였다. 또한 검보정 전후에 대한 기저유량을 비교하기 위하여 SWAT Output Data를 이용하여 유역에 대한 지표수유출, 중간유출, 지하수유출 등을 추출하였다. 추출한 단위면적당 데이터를 단위환산을 통해 유출량으로 산정하였으며 검보전 전과 데이터를 비교하였다. 지표수-지하수를 고려한 통합적 해석의 어려움과 실측치의 부족, 분석에 대한 불확실성 등으로 기저유량에 대한 해석은 어렵지만 SWAT-CUP을 이용하여 검보정 및 불확실성 개선이 수행되면 좀더 정확한 유량을 계산할 수 있으며 이는 향후 연구지역 지표수-지하수 연계해석을 위한 기초자료로 활용될 수 있을 것으로 판단된다.

• Journal of Korean Society on Water Environment
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• v.28 no.4
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• pp.595-600
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• 2012

This study is to assess the application of SWAT-CUP(Soil and Water Assessment Tool-Calibration Uncertainty Programs) and to extend daily flow data from 8-day interval flow data which has been measured by Korean Ministry of Environment(MOE). Model sensitivity analysis and calibration were performed with sequential uncertainty fitting(SUIF-2), which is one of the programs interfaced with SWAT, in the package SWAT-CUP. The most sensitive parameters were SOL_K.sol, CH_N2.rte, CN2.mgt, SOL_BD.sol, ALPHA_BF.gw, ALPHA_BNK.rte, SOL_AWC.sol, CH_K2.rte, SFTMP.bsn, GW_DELAY.gw. Following the sensitivity analysis, SWAT-CUP calibration was carried out using 8-day interval flow data from January 2008 to December 2010. The results were then assessed based on the visual agreement and simulated flow plots and the performance statistics generated $R^2$ and NSE which are 0.71 and 0.61 respectively. Results of these statistics indicated that there was a good agreement between the observed and simulated flow. To extend daily flow data from 8-day interval flow data, parameters, which were estimated by SWAT-CUP, re-entered for SWAT model. As a result, the observed flow data were found to reflect the trend of simulated flow data. From these results, it is thought that this method could be used to provide daily flow data using 8-day interval flow data.

• Ecology and Resilient Infrastructure
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• v.3 no.1
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• pp.35-45
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• 2016

The correlation relationships and their corresponding equations between the geomorphological parameters and the Soil Water Assessment Tool (SWAT) model parameters by Sequential Uncertainty Fitting - version 2 (SUFI-2) algorithm of SWAT Calibration and Uncertainty Programs (SWAT-CUP) were developed at the Seom-river experimental watershed. The parameters of the SWAT model at the Soksa-river experimental watershed were estimated by the developed equations. The SWAT model parameters were estimated by SUFI-2 algorithm of SWAT-CUP with rainfall-runoff data from the Soksa-river experimental watershed from 2000 to 2007. Rainfall-runoff simulation of the SWAT model was carried out at the Soksa-river experimental watershed from 2000 to 2007 for the applicability of the estimated parameters by the developed equations. The root mean square errors (RMSE) between the observed and the simulated rainfall-runoffs using the estimated parameters by developed equations of correlation analysis and the optimum parameters by SUFI-2 of SWAT-CUP were $1.09m^3/s$ and $0.93m^3/s$ respectively at the Soksa-river experimental watershed from 2000 to 2007. Therefore, it is considered that the parameter estimation of the SWAT model by the geomorphological characteristics parameters has applicability.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.314-314
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• 2020

SWAT (Soil and Water Assessment Tool)은 미국 농무성 농업연구소에서 개발된 준분포형(semi-distributed) 수문 모형으로 복합토지이용유역에서 장기간에 걸친 다양한 종류의 토양, 토지이용 및 토지관리 상태의 변화에 따른 유역의 유출량, 유사량 및 영양물질의 영향을 예측하기 위해 개발되었다. SWAT은 기본적으로 다양한 매개변수에 대한 수동 보정 기능을 제공하고 있지만 매개변수 보정에 따른 모의결과의 불확실성을 수반하게 된다. 이러한 문제를 해결하기 위해 자동보정 기능을 제공하는 SWAT-CUP (Calibration and Uncertainty Program)이 개발되었다. SWAT-CUP에서 제공하는 매개변수의 최적화 과정에서 유사한 모의 결과를 산출하는 수천 개의 매개변수조합이 존재하기 때문에 보정기법의 선택에 따라 최종 매개변수의 값이 달라질 수 있다. 불확실성을 발생시키는 요인으로 (1) 매개변수의 선택, (2) 보정 기법, (3) 목적함수, (4) 매개변수의 초기 범위, (5) 모의(simulation)의 실행(run) 및 반복(iteration) 횟수, (6) 위치, 개수 등 보정 자료의 선택 등이 주로 지목된다. 이러한 요인으로 발생하는 불확실성은 SWAT 모형의 구조 및 입력 자료에서 기인하는 것으로, 사용자의 설정에 따라 크게 좌우된다. 본 연구에서는 SWAT 매개변수 보정 과정에서 발생할 수 있는 불확실성을 평가하고, 효율적인 보정 방안을 제시하기 위해 수행되었다. 낙동강 권역의 내성천 유역을 대상으로 SWAT 모형을 구축하였으며, 내성천 본류에 위치한 수위(유량) 관측소의 자료를 활용하여 검·보정을 수행하였다. 모의 결과는 유량의 크기 뿐 아니라 유량의 발생 시기, 유역의 반응 및 증가·감소 경향성을 함께 고려하여 평가하였다. 그 결과 모형 구조에 따른 불확실성의 전이과정을 정확하게 파악하는 것은 불가능하지만 SWAT 모형의 비고유성(non-uniqueness)에 의한 불확실성을 정량화하여 나타내었다.

• Journal of Korea Water Resources Association
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• v.44 no.9
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• pp.711-720
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• 2011

SWAT (Soil and Water Assessment Tool) model was calibrated for the flow rate of the Deachung lake with a large area of 3108.29 $km^2$. Application of SWAT model requires significant number of input data and is prone to result in uncertainties due to errors in input data, model structure and model parameters. The SUFI-2 (Sequential Uncertainty Fitting Ver. 2) program and GLUE (Generalized Likelihood Uncertainty Estimation) program in SWAT-CUP (SWAT-Calibration and Uncertainty Program) are used to select the best parameters for SWAT model. Optimal combination of parameter values was determined through 2,000 iterative SWAT model runs. The Nash-Sutcliffe values and $R^2$ values were 0.87 and 0.89 respectively indicating both methods show good agreements with observed data successfully. RMSE and MSE values also showed similar results for both programs. It seems the SWAT-CUP has a great practical appeal for parameter optimization especially for large basin area and it also can be used for less experienced SWAT model users.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.529-536
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• 2013

The semi-distributed rainfall runoff model of SWAT is applied to the Seom-river experimental watershed. The simulations of various antecedent periods before the targeted simulation periods of 2002 to 2009 are not necessary despite of the slight appearance of corresponding changes in simulated total runoff. The simulated results of total runoff by using various numbers of soil layer maps have little differentiated nevertheless the slight changes in simulated results have been appeared. The 7 parameters of CANMX, $CN_2$, ESCO, GW_REVAP, SOL_ALB, SOL_AWC, and SOL_K greatly govern the rainfall runoff are confirmed and their sensitivity analyses have been carried out. The optimal parameters used in SWAT are derived by SUFI-2 of SWAT-CUP. The NS and $R^2$ are 0.99 and 0.98, respectively which is shown the good agreement between the observed and the simulated results. The uncertainty factors of P-factor and R-factor are 0.85 and 0.06, respectively which is also shown the high efficiency of the model. The high applicability is also shown with improving the RMSE in SWAT model simulation using the parameters estimated by SUFI-2 of SWAT-CUP.

• Journal of Korea Water Resources Association
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• v.53 no.12
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• pp.1143-1157
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• 2020

In this study, a criteria for the SWAT model calibration method in SWAT-CUP which considers multi-site and multi-variable observations was presented. For its application, the SWAT model was simulated using long-term observed flow, soil moisture, and evapotranspiration data in Yongdam study watershed, investigating the hydrological runoff characteristics and water balance in the water cycle analysis. The model was calibrated with different parameter values for each sub-watershed in order to reflect the characteristics of multiple observations through one-by-one calibration, appropriate settings of model simulation run/iteration number (1,000 simulation runs in the first iteration and then 500 simulation runs for the following iterations), and executions of partial and all run in SWAT-CUP. The flow simulation results of watershed outlet point, ENS 0.85, R2 0.87, and PBIAS -7.6%, were compared with the analysis results (ENS 0.52, R2 0.54, and PBIAS -22.4%) applied in the other batch (i.e., non one-by-one) calibration approach and showed better performances of proposed method. From the simulation results of a total of 15 years, it was found that the total runoff (streamflow) and evapotranspiration rates from precipitation are 53 and 39%, and the ratio of surface runoff and baseflow (i.e., sum of lateral and return flow, and recharge deep aquifer) are 35 and 65%, respectively, in Yongdam watershed. In addition, the analytical amount of available water (i.e., water yield), including the total annual streamflow (daily average 21.8 m3/sec) is 6.96 billion m3 per year (about 540 to 900 mm for sub-watersheds).

• Journal of Korea Water Resources Association
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• v.53 no.1
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• pp.45-56
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• 2020

This study aims to quantify the uncertainty that can be induced by the objective function when calibrating SWAT parameters using SWAT-CUP. SWAT model was constructed to estimate runoff in Naesenong-cheon, which is the one of mid-watershed in Nakdong River basin, and then automatic calibration was performed using eight objective functions (R², bR², NS, MNS, KGE, PBIAS, RSR, and SSQR). The optimum parameter sets obtained from each objective function showed different ranges, and thus the corresponding hydrologic characteristics of simulated data were also derived differently. This is because each objective function is sensitive to specific hydrologic signatures and evaluates model performance in an unique way. In other words, one objective function might be sensitive to the residual of the extreme value, so that well produce the peak value, whereas ignores the average or low flow residuals. Therefore, the hydrological similarity between the simulated and measured values was evaluated in order to select the optimum objective function. The hydrologic signatures, which include not only the magnitude, but also the ratio of the inclining and declining time in hydrograph, were defined to consider the timing of the flow occurrence, the response of watershed, and the increasing and decreasing trend. The results of evaluation were quantified by scoring method, and hence the optimal objective functions for SWAT parameter calibration were determined as MNS (342.48) and SSQR (346.45) with the highest total scores.

• Journal of Korean Society on Water Environment
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• v.28 no.3
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• pp.347-358
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• 2012

The SWAT (Soil and Water Assessment Tool) should be calibrated and validated with observed data to secure accuracy of model prediction. Recently, the SWAT-CUP (Calibration and Uncertainty Program for SWAT) software, which can calibrate SWAT using various algorithms, were developed to help SWAT users calibrate model efficiently. In this study, three algorithms (GLUE: Generalized Likelihood Uncertainty Estimation, PARASOL: Parameter solution, SUFI-2: Sequential Uncertainty Fitting ver. 2) in the SWAT-CUP were applied for the Soyang-gang dam watershed to evaluate these algorithms. Simulated total streamflow and 0~75% percentile streamflow were compared with observed data, respectively. The NSE (Nash-Sutcliffe Efficiency) and $R^2$ (Coefficient of Determination) values were the same from three algorithms but the P-factor for confidence of calibration ranged from 0.27 to 0.81 . the PARASOL shows the lowest p-factor (0.27), SUFI-2 gives the greatest P-factor (0.81) among these three algorithms. Based on calibration results, the SUFI-2 was found to be suitable for calibration in Soyang-gang dam watershed. Although the NSE and $R^2$ values were satisfactory for total streamflow estimation, the SWAT simulated values for low flow regime were not satisfactory (negative NSE values) in this study. This is because of limitations in semi-distributed SWAT modeling structure, which cannot simulated effects of spatial locations of HRUs (Hydrologic Response Unit) within subwatersheds in SWAT. To solve this problem, a module capable of simulating groundwater/baseflow should be developed and added to the SWAT system. With this enhancement in SWAT/SWAT-CUP, the SWAT estimated streamflow values could be used in determining standard flow rate in TMDLs (Total Maximum Daily Load) application at a watershed.

• Journal of Korea Water Resources Association
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• v.53 no.5
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• pp.347-356
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• 2020

The main objective of the study is to propose the most efficient SWAT model calibration method using SWAT-CUP with less computing time and high performance. In order to achieve the goal, Case1-3 (250, 500, and 1,000 simulation runs) and Case4 (1,000 simulation runs in the first iteration and then 500 simulation runs for the following iterations) were defined to compare the results. When evaluating the values of the objective function, Case2 and Case3 reached the same value after the fourth iteration, and Case1 reached the closed value of Case2-3 after the eighth iteration. However, the final estimates of the parameters had different ranges in Cases1-3, and only the results of Case3 and Case4 converged similarly. Thus, it can be considered that the parameter calibration results are highly affected by the initial number of simulation runs. On the other hand, SWAT simulation results did not show the significant difference after the first iteration, unlike the parameter ranges. From the analysis results, we can conclude that the most suitable and effective method was to repeat one or two times of iterations with a sufficient number of simulation runs, as in Case4.