• Journal of Korean Society on Water Environment
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• v.27 no.3
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• pp.264-272
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• 2011

The objective of this study was to develop a model for predicting long-term runoff in a basin using the ensemble streamflow prediction (ESP) technique and review its reliability. To achieve the objective, this study improved not only the ESP technique based on the ensemble scenario analysis of historical rainfall data but also conventional ESP techniques used in conjunction with qualitative climate forecasting information, and analyzed and assessed their improvement effects. The model was applied to the Geum River basin. To undertake runoff forecasting, this study tried three cases (case 1: Climate Outlook + ESP, case 2: ESP probability through monthly measured discharge, case 3: Season ESP probability of case 2) according to techniques used to calculate ESP probabilities. As a result, the mean absolute error of runoff forecasts for case 1 proposed by this study was calculated as 295.8 MCM. This suggests that case 1 showed higher reliability in runoff forecasting than case 2 (324 MCM) and case 3 (473.1 MCM). In a discrepancy-ratio accuracy analysis, the Climate Outlook + ESP technique displayed 50.0%. This suggests that runoff forecasting using the Climate Outlook +ESP technique with the lowest absolute error was more reliable than other two cases.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.25 no.3
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• pp.97-111
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• 2022

This study was conducted as restoration work to improve the discharge in forested wetlands where there is a concern of damage and observed changes in the discharge and groundwater level. The monthly changes showed that during the wet season, the amount of discharge decreased after restoration and GWL increased. It showed that during the dry season, the GWL and discharge increased. The increased discharge after restoration seems to be the difference in the number of days with no rainfall duration. The change in discharge for each unit of rainfall showed a tendency to increase the baseflow and decrease the direct discharge after restoration. The recharge ratio of GWL showed a decreasing tendency as rainfall was higher. After restoration, it showed a higher tendency under rainfall with less than 20mm. It has been confirmed that the restoration implemented by the study caused such an effect as the increased baseflow and increased GWL. It would be an effective restoration method to maintain water resources in forested wetlands. In the initial rainfall, it demonstrated a certain level of effect, but it is necessary to develop a restoration technology that can decrease the amount of water discharged after the end of rainfall or during the period of no rainfall to protect and maintain the forested wetlands. Streamflow should be identified by each type of terrain of wetlands and a proper restoration countermeasure should be devised for the site where the discharge frequently occurs.

• Journal of Korea Water Resources Association
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• v.40 no.2 s.175
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• pp.147-158
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• 2007

This study attempted to determine a suitable hydrologic model for assessing the impact of climate change on water resources, and to assess the accuracy of streamflow scenarios simulated by the selected hydrologic model using the meteorological scenarios of the Seoul National University Regional Climate Model(SNURCM). Comparison of four water balance models and two daily conceptual rainfall-runoff models for the simulation capability of the Daecheong Dam inflow indicated that the abcd model performs the best among the tested water balance models and performs as well as SSARR that is popular as a daily rainfall-runoff model in Korea. Parameters of the abcd model were then estimated for 12 ungauged subbasins of the Geum River by the regionalization method. The model parameters were first calibrated at nine multi-purpose dams and were then regionalized using catchment characteristics for another four multi-purpose dams, which were assumed to be ungauged sites. The model efficiency(ME) coefficients of the simulated inflows for these four dams were at least 87%. The MEs of the hindcasted meteorological rainfall scenarios of the 12 subbasins of the Geum River were more than 60%. Moreover, the ME of the Daecheong Dam inflow simulated by the abcd model using the SNURCM rainfall scenarios was more than 80%. Therefore, this research concluded that the abcd model coupled with the SNU-RCM meteorological scenarios can be used for impact assessment studies of climate change on water resources.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2B
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• pp.107-120
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• 2010

The effect of potential future climate change on the inflow of agricultural reservoir and its impact to downstream streamflow by reservoir operation for paddy irrigation water was assessed using the SLURP (semi-distributed land use-based runoff process), a physically based hydrological model. The fundamental input data (elevation, meteorological data, land use, soil, vegetation) was collected to calibrate and validate of the SLURP model for a 366.5 $km^2$ watershed including two agricultural reservoirs (Geumgwang and Gosam) located in Anseongcheon watershed. Then, the CCCma CGCM2 data by SRES (special report on emissions scenarios) A2 and B2 scenarios of the IPCC (intergovernmental panel on climate change) was used to assess the future potential climate change. The future weather data for the year, m ms, m5ms and 2amms was downscaled by Change Factor method through bias-correction using 3m years (1977-2006) weather data of 3 meteorological stations of the watershed. In addition, the future land uses were predicted by modified CA (cellular automata)-Markov technique using the time series land use data fromFactosat images. Also the future vegetation cover information was predicted and considered by the linear regression between monthly NDVI (normalized difference vegetation index) from NOAA AVHRR images and monthly mean temperature using eight years (1998-2006) data.

• Korean Journal of Ecology and Environment
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• v.40 no.1
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• pp.155-162
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• 2007

Water balance is the major factor in forest ecosystem, and is closely related to the vegetation and topographic characteristics within a watershed. The hydrologic response of a forest watershed was investigated with the hydrological model. The deterministic, lumped parameter model (BROOK90) was selected and used to evaluate the applicability of the model for simulating daily runoff on the steep, forested watershed. The model was calibrated and validated against the streamflow data measured at the Bukmoongol watershed. The deviation in runoff volume $(D_v)$ was -1.7% for the calibration period, and the $D_v$ value for the validation period was 4.6%. The correlation coefficient (r) and model efficiency (E) on monthly basis were 0.922,0.847, respectively, for the calibration period, while the r- and E-value for the validation period were 0.941, 0.871, respectively. Overall, the simulated streamflows were close to the observations with respect to total runoff volume, seasonal runoff volume, and baseflow index for the simulation period. BROOK90 model was able to reproduce the trend of runoff with higher correlation during the simulation period.

• Journal of Korea Water Resources Association
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• v.40 no.5
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• pp.419-430
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• 2007

Integrated modelling of surface water and groundwater has become important to satisfy the growing demands for sustainable water resources and improved water quality. In this study, the integrated model of the semi-distributed watershed model, SWA T and the fully-distributed groundwater flow model, MODFLOW is applied to Musirn river basin for the purpose of investigating its applicability to reproduce watershed-scale hydrological processes. This objective is accomplished by first demonstrating good agreement between the simulated discharge hydrographs with the measured hydrographs for the period of 2001 -2004 while simultaneously calibrating the calculated groundwater level distribution to observation wells. Next, the integrated model is used to evaluate the effect of different temporal precipitation averages on hydrodynamic processes of streamflow, percolation, recharge and groundwater discharge. Moreover, comprehensive simulations are performed to present the relationships between monthly precipitation and each hydrological component, and to analyze the temporal-spatial variability of recharge. The results show that the components are highly interrelated, and that the heterogeneity of watershed characteristics such as subbasin slope, land use, soil type causes a significant spatial variation of recharge. Overall it is concluded that the model is capable of reproducing the temporally and spatially varied surface and subsurface hydrological processes at the watershed scale.

• Journal of Korea Water Resources Association
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• v.49 no.5
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• pp.361-372
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• 2016

Reliable long-term dam inflow prediction is necessary for efficient multi-purpose dam operation in changing climate. Since 2000s the teleconnection between global climate indices (e.g., ENSO) and local hydroclimate regimes have been widely recognized throughout the world. To date many hydrologists focus on predicting future hydrologic conditions using lag teleconnection between streamflow and climate indices. This study investigated the utility of teleconneciton for predicting dam inflow with 1-month lead time at Andong dam basin. To this end 40 global climate indices from NOAA were employed to identify potential predictors of dam inflow, areal averaged precipitation, temperature of Andong dam basin. This study compared three different approaches; 1) dam inflow prediction using SWAT model based on teleconneciton-based precipitation and temperature forecast (SWAT-Forecasted), 2) dam inflow prediction using teleconneciton between dam inflow and climate indices (CIR-Forecasted), and 3) dam inflow prediction based on the rank of current observation in the historical dam inflow (Rank-Observed). Our results demonstrated that CIR-Forecasted showed better predictability than the other approaches, except in December. This is because uncertainties attributed to temporal downscaling from monthly to daily for precipitation and temperature forecasts and hydrologic modeling using SWAT can be ignored from dam inflow forecast through CIR-Forecasted approach. This study indicates that 1-month lead dam inflow forecast based on teleconneciton could provide useful information on Andong dam operation.

• Journal of Environmental Impact Assessment
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• v.27 no.3
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• pp.267-278
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• 2018

With climate change and population growth, there are significant increases in water scarcity. There have been water security assessments to abate the gap between water demand and availability to support water resource management. However, most of the assessments are focusing on the water that flows through either on or below the land surface, failing to consider water that infiltrates and can be used by vegetation. This study presents water scarcity assessment accounting for Blue and Green water concept, and applied the method to Boryung region. Monthly streamflow, evapotranspiration, and soil moisture were estimated by SWAT modeling, and each of them was used to analyze Blue and Green water scarcity. Blue and Green water scarcity had different aspect, and the result indicated the time when water scarcity is more likely to happen. The water scarcity assessment framework presented in this paper provides novel assessment method integrating hydrologic and ecosystem aspects, thereby improving the understanding of how water resources should be managed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.5
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• pp.477-484
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• 2021

Due to climate change, parts of Korea are experiencing large and small droughts every 2-3 years and extreme droughts every 7 years. Since most droughts occur mainly in areas where small water supply facilities in the tributaries or upstream are located, more research on technology for securing water in these areas is required. In this study, a drought evaluation using SPEI (Standardized Precipitation Evapotranspiration Index), SDI (Streamflow Drought Index), and WBDI (Water Budget-based Drought Index) was performed to investigate hydrological drought in the Mulrocheon watershed of Chuncheon, a vulnerable area in terms of water supply. As a result of calculating hydrological drought indices SPEI and SDI, examining each duration, it was confirmed that the common drought in 2014 did not recover and continued until 2015. In the hydrological drought index evaluation result by WBDI, a very severe drought condition was observed in the spring of 2015 following 2014, and that drought was the most severe at -1.94 in November 2017. As a result of deriving a SDF (Severity-Duration-Frequency) curve through frequency analysis by duration using the drought index calculated on a monthly basis from 2003 to 2019 (17 years), most droughts in the Mulrocheon watershed were found to have a return period of less than 10 years, but droughts that occurred in 2014, 2015, and 2019 were found to cover more than 20 years, respectively.

• Journal of Korea Water Resources Association
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• v.47 no.2
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• pp.145-159
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• 2014

This study is to evaluate the future climate change impact on turbidity water and eutrophication for Chungju Lake by using CE-QUAL-W2 reservoir water quality model coupled with SWAT watershed model. The SWAT was calibrated and validated using 11 years (2000~2010) daily streamflow data at three locations and monthly stream water quality data at two locations. The CE-QUAL-W2 was calibrated and validated for 2 years (2008 and 2010) water temperature, suspended solid, total nitrogen, total phosphorus, and Chl-a. For the future assessment, the SWAT results were used as boundary conditions for CE-QUAL-W2 model run. To evaluate the future water quality variation in reservoir, the climate data predicted by MM5 RCM(Regional Climate Model) of Special Report on Emissions Scenarios (SRES) A1B for three periods (2013~2040, 2041~2070 and 2071~2100) were downscaled by Artificial Neural Networks method to consider Typhoon effect. The RCM temperature and precipitation outputs and historical records were used to generate pollutants loading from the watershed. By the future temperature increase, the lake water temperature showed $0.5^{\circ}C$ increase in shallow depth while $-0.9^{\circ}C$ in deep depth. The future annual maximum sediment concentration into the lake from the watershed showed 17% increase in wet years. The future lake residence time above 10 mg/L suspended solids (SS) showed increases of 6 and 17 days in wet and dry years respectively comparing with normal year. The SS occupying rate of the lake also showed increases of 24% and 26% in both wet and dry year respectively. In summary, the future lake turbidity showed longer lasting with high concentration comparing with present behavior. Under the future lake environment by the watershed and within lake, the future maximum Chl-a concentration showed increases of 19 % in wet year and 3% in dry year respectively.