Performance evaluation of the national 7-day water forecast service

Abstract

The Bureau of Meteorology launched a deterministic 7-day streamflow forecast service to the public in September, 2015. These streamflow forecasts indicate likely river flow conditions in the coming week. The service has been developed mainly to assist river managers in making informed decisions about water resources management to ensure the best use is made, both from agricultural and environmental perspectives. The service currently provides daily updates of daily volume forecasts to the public for 132 locations across Australia (Figure 1). This paper investigates the performance of the operational 7-day streamflow forecasts at targeted 53 locations across Australia. Evaluating operational forecast performance is essential to identify forecast discrepancies in order to improve the service. Performance metrics for rainfall and streamflow were investigated. Operational streamflow forecasts for more than 90% of the selected 53 locations exceed a set criterion of positive mean absolute error skill score up to 3-days lead-time. Unreliable or poor quality input data was the main cause of suboptimal performance for the remaining 10% of locations. Forecast performance for perennial streams is found to outperform those in ephemeral streams. The inability of hydrological model structure to cope with complex and highly non-linear hydrological processes in dry areas is seem to be the cause for suboptimal streamflow forecasts. Forecast performance at locations with large catchment areas show better skills than other locations having small catchment areas.