Highly concentrated precipitation during the rainy season poses challenges to the South Korean water resources management in efficiently storing and redistributing water resources. Under the new climate regime, water resources management is likely to become more challenging with regards to water-related disaster risk and deterioration of water quality. To alleviate such issues by adjusting management plans, this study examined the impact of climate change on the streamflow in the Bocheongcheon basin of the Geumgang river. A globally accepted hydrologic model, the HEC-HMS model, was chosen for the simulation. By the calibration and the validation processes, the model performance was evaluated to range between “satisfactory” and “very good”. The calibrated model was then used to simulate the future streamflow over six decades from 2041 to 2100 under RCP4.5 and RCP8.5. The results indicated significant increase in the future streamflow of the study site in all months and seasons over the simulation period. Intensification of seasonal differences and fluctuations was projected under RCP 8.5, implying a challenge for water resources managers to secure stable sources of clean water and to prevent water-related disasters. The analysis of the simulation results was applied to suggest possible local adaptive water resources management policy.

In Korea, where more than half of annual precipitation (55%, 653.9 mm) occurs during the rainy season (June ~ September), it is difficult to efficiently store and manage water resources. These challenges are likely to be exacerbated by climate change, the impact of which was demonstrated in the summer of 2020 in the form of an unprecedented long rainy season. The purpose of this study is to help establish efficient future water resource management and water-related disaster prevention measures in response to climate change. Application of the HEC-HMS (Hydrologic Engineering Center’s Hydrologic Modeling System) model was evaluated for simulation of rainfall runoff for the Daecheong Dam basin. During model set-up, parameter values for loss, transform and routing methods were calculated based on land cover/land use status and soil type. The calibration results for rainfall runoff at Junction-22 for the year of 2008 showed an excellent Nash-Sutcliffe Efficiency (NSE) value of 0.732, proving the high accuracy of the model. Simulation results for runoff volume at the same junction in 2017 using calibrated parameter values showed an acceptable NSE value of 0.535. Thus, the overall model efficiency of HEC-HMS was validated. The results of a pilot simulation of the impact of climate change on runoff volume under RCP scenarios 4.5 and 8.5 for the year 2050 forecast potential exacerbation of the seasonality in precipitation, in addition to showing a dissimilar pattern from the present, suggesting potential water management issues. Since future management methods should take into account the intensity and frequency of precipitation during the dry and rainy seasons, which vary due to climate change, validation of the HEC-HMS as a tool for predicting runoff volume in the mid- to long-term future is important.