The New Zealand Wave Climate Derived from Buoy, Satellite and Hindcast Data

The limited availability of long-term wave data presents a challenge in assessing the wave climate around the New Zealand coast, particularly when it comes to determining extreme wave statistics. In this paper we discuss the use of numerical modelling to provide wave climate information, supplementing data from wave buoys and satellite altimeter sources. A 20-year hindcast of wave conditions in the Southwest Pacific and Southern Oceans from 1979 through 1998 has been created using the WAM model. Input winds for the model were derived from the European Centre for Medium Range Weather Forecasts (ECMWF). The hindcasts were compared with data from wave buoy deployments at representative sites around the New Zealand coast. At four deep-water sites (90-120 m), scatter indices (ratio of root mean square error to mean) in comparisons between measured and hindcast significant heights averaged 0.28. Mean significant wave heights from the hindcast were generally 0.3-0.5 m lower than corresponding data from altimeters flown on the TOPEX/Poseidon and ERS1 and 2 satellite missions. Occurrence distributions of significant wave height from the hindcast matched satellite data at the lowest wave heights and above the peaks of the distributions, but tended to overestimate occurrence below the peak and underestimate the occurrence of the largest wave events. We discuss methods used to determine extreme wave statistics from the comb ined records. Other wave climate features were investigated. Annual cycles of mean wave height were identified throughout the region, and longer-term variations were also noted in the form of correlations with the El Ni o/Southern Oscillation.