Verification of RiCOM for Storm Surge Forecasting

Abstract

RiCOM is an unstructured-grid finite-element coastal ocean model. It is used to provide storm surge forecasts as part of a larger suite of environmental forecasting models known collectively as EcoConnect. RiCOM is forced with surface pressure and with 10 m winds forecast by the weather prediction model, NZLAM-12. Our objective is to evaluate the RiCOM forecasts, to understand the strengths of the model, and to identify improvements that can be made. The verification process involves comparison of the predicted sea level with data gathered from the New Zealand-wide sea level network managed by NIWA. Predicted time series for each site are built up from successive 48-hour forecasts. Different forcing and frequency components of the real and model time series are then compared. Historical mooring data are also used to evaluate RiCOM's ability to capture flows. Tidal and low frequency components of RiCOM are seen to compare well with sea level network data. There are some situations where RiCOM does not perform as well. Velocity forecasts have only been basically evaluated due to a lack of current data. Future additions and improvements to the model have been identified such as improving the wind stress formulation, extending the model to three dimensions, and adding baroclinic circulations and coupling the model with a wave model.