This research aims to predict long-term rainfall-runoff flow using the 1-month, 3-month ensemble forecasts (precipitation, temperature, etc.) of GloSea5 (Global Seasonal forecasting system version 5) that was jointly developed and is being operated by the KMA and the UK's Met Office. These data were modified using statistical downscaling method and were converted into inputs for hydrological model, K-DRUM (K-water Distributed Rainfall Runoff Model). Case studies were conducted in two basins: Yongdam Dam and the Namkang Dam watersheds, which are located at the upper stream basin, making it relatively easy to analyze and evaluate rainfall-runoff flow. After evaluating hydrologic model performance and the precipitation forecast levels for the period of GloSea5's HCST (Hindcast; 1996 to 2009), the data for GloSea5's FCST (Forecast; 2014 to 2015) were used to evaluate the long-term rainfall-runoff flow prediction using the K-DRUM model.
The results showed appropriate outcomes of reproducibility for rainfall and runoff compared to specifically designated years in the past and presented similar results in the forecast as well. Therefore, this research approach can be applied to a long-term water management, particularly for the planning of dam reservoir operations in order to secure stable water supply.