Long-Term Rainfall-Runoff Flow Prediction Using GloSea5 System Based on Meteorological Forecasts and Distributed Hydrologic Model (K-DRUM)

Along with a recent climate change, the uncertainty regarding precipitation levels and the frequency and severity of floods, droughts, and other natural disasters has increased. This makes raise the awareness in the social needs for stable water management and leads a greater demand for meteorological forecasts for water supply and flood control. Typically, water management for stable water supply requires long-term meteorological forecasts including monthly, seasonal and annual data. In Korea, although the Korea Meteorological Administration (KMA) provides probabilistic long-term forecasts, they could not be used for the hydrological forecasting model directly since they are unsuitable to utilize for water resource management. As such, a water management plan which connects the KMA's probabilistic long-term forecasts and hydrological forecasting model is needed for long-term water management.

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.