To investigate the recent effects of climate change in the upper Geum River basin in South Korea, a detailed trend analysis of 17 extreme climate indices based on 33 years (1988–2020) of daily precipitation, and daily (minimum and maximum) temperature data has been analyzed in this study. Out of the 17 extreme climate indices, nine (eight) indices were based on temperature (precipitation) data. Trend analysis based on detailed temporal scales (annual, seasonal, monthly) were performed through the Mann–Kendall trend test and the Theil–Sen slope method. Furthermore, the Mann–Whitney–Pettit test was also applied in this study, to detect abrupt changes in the extreme climate indices. Based on the results of this study, the climate conditions at the upper Geum River basin for the past three decades can be summarized as follows: general increase in temperature intensity, decrease in cold duration, increased heat duration, increased precipitation intensity, and increased consecutive wet and dry durations. Furthermore, a prolonged summer season (shorter spring, and autumn periods) and precipitation shifts, were detected based on trend analysis results of seasonal, and monthly time scales. The results presented in this study can provide supplementary data for improving watershed management strategies in the upper Geum River basin.

Precipitation is a significant input variable required in hydrological models such as the Soil & Water Assessment Tool (SWAT). The utilization of inaccurate precipitation data can result in the poor representation of the true hydrologic conditions of a catchment. SWAT utilizes the conventional nearest neighbor method in assigning weather parameters for each subbasin; a method inaccurate in representing spatial variations in precipitation over a large area, with sparse network of gauging stations. Therefore, this study aims to improve the spatial variation in precipitation data to improve daily streamflow simulation with SWAT, even pre-model calibration. The daily streamflow based on four interpolation methods, nearest neighbor (default), inverse-distance-weight, radial-basis function, and ordinary kriging, were evaluated to determine which interpolation method is best represents the precipitation at Yongdam watershed. Based on the results of this study, the application of spatial interpolation methods generally improved the performance of SWAT to simulate daily streamflow even pre-model calibration. In addition, no universal method can accurately represent the long-term spatial variation of precipitation at the Yongdam watershed. Instead, it was observed that the optimal selection of interpolation method at the Yongdam watershed is dependent on the long-term climatological conditions of the watershed. It was also observed that each interpolation method was optimal based on certain meteorological conditions at Yongdam watershed: nearest neighbor for cases when the occurrence probability of extreme precipitation is high during wet to moderately wet conditions; radial-basis function for cases when the number of dry days were high, during wet, severely dry, and extremely dry conditions; and ordinary kriging or inverse-weight-distance method for dry to moderately dry conditions. The methodology applied in this study improved the daily streamflow simulations at Yongdam watershed, even pre-model calibration of SWAT.

This study developed a disaster assessment system, which integrated flood inundation, risk analysis system, and a decision support system. The parameter representation of the model was selected through sensitivity analysis, used for automated parameter optimization of the model. The Bocheong watershed in South Korea was selected for this study. The results of the simulation were used for disaster assessments; estimated results were calculated basing from flood damages from historical flood disasters, GIS, population, and inundation results. Lastly, this study developed a user-support system to provide real-time meteorological and hydrological data to local government and disaster situation room in South Korea. From the results of the evaluation, the developed model in this study was proven to be more excellent than ModClark model. The application of this model was found superior for ungaged basin such as mountainous area and small creek basins.

Reservoirs are essential structures to provide reliable water supply, hydropower, and flood control. Climate change could be a significant factor that increases the sediment yield leading to rapid reduction of the reservoir’s storage capacity and design life. Previous studies of reservoir sedimentation-related impact of climate change often coupled a hydrological model with the raw outputs of general circulation model (GCM)/regional circulation model (RCM), which shows bias when comparing with observations data. This study aims to integrate the soil and water assessment tool (SWAT) model with 14 bias-corrected GCM/RCM models under two emissions scenarios, representative concentration pathway (RCP) 4.5 and 8.5, applied to Pleikrong reservoir to estimate its sedimentation in the long term period. The results show the reduction in reservoir storage capacity due to sedimentation ranges from 25% to 62% by 2050, depending on the defferent climate change models. The reservoir reduced storage volume’s rate in considering the impact of climate change is much faster than in the case of no climate change. The outcomes of this study will be helpful for a sustainable and climate-resilient plan of sediment management for the Pleikrong reservoir.

Levees are facilities constructed along river to protect floodplains against flooding. However, levee failures are also possible if seepage reaches landside surface of the levee. The seepage on the surface of the landside slope can be prevented by efficient design of levee drainage systems. This study aims to show the seepage control potential on levees by installation of perforated drainpipes, which was verified through hydraulic experiments. Scenarios were performed with four different water stages at riverside. For each scenario, the piezometric heads located at the bottom of the experimental levee were measured. The results of the hydraulic experiments showed that the precise positioning of perforated drainpipes is vital since it greatly affects the amount of seepage in the levee. The SEEP/W model that was calibrated and verified with the experiment results was used to suggest appropriate installation location range of the perforated drainpipe. From the numerical simulation, as the central location of perforated drainpipe is closer to landside levee toe horizontally and to foundation surface vertically, the safety of levee was increased from the seepage failure.