Development of long-term rainfall and inflow forecasting for reservoir watersheds in taiwan

The long-term inflow forecasts can be used to estimate the future storage of reservoir to support decision making for preparing drought-resistance actions in advance during the dry period. The article introduces the development and evolution of long-term rainfall and inflow forecasting for Taiwanʼs key reservoir catchments. By optimizing the long-term rainfall and temperature forecasts of the Central Meteorological Bureau combined with the hydrological model, the long-term inflow forecasts for reservoirs are carried out. Three versions of long-term inflow forecasting have been developed. The main difference among the three versions is the use of different rainfall and temperature forecasts and downscaling methods. The first version uses the seasonal weather outlook to generate rainfall and temperature forecasts. The second version maps the forecasts by TCWB2T2 from the weather stations of flatland to the reservoir catchments. The third version downscales the grid-based forecasts by TCWB1T1 (a coupled ocean-atmosphere general circulation model) to the reservoir catchments. The generated/mapped/downscaled rainfall and temperature forecasts are then input into the hydrological model with an ensemble optimization method to carry out the 1 to 6– months-ahead inflow forecasting for each reservoir. Based on the results of effectiveness evaluation, the forecast accuracy improves with the evolution of version. © 2021, Taiwan Agricultural Engineers Society. All rights reserved.