SA-West Marine Heat Waves V1.0

Marine heatwaves (MHWs) are discrete, prolonged periods of anomalously warm ocean temperature that reorganize ecosystems, disrupt fisheries and aquaculture, and alter biogeochemical processes. In our workflow we follow Hobday et al. (2016): from each daily temperature series we form a smoothed seasonal climatology (“seas”) and a smoothed 90th-percentile threshold (“thresh”) over a fixed climatology period; an MHW is declared when temperature exceeds the daily threshold for ≥5 consecutive days, permitting short gaps to be bridged, and for each event we compute start/peak/end dates, duration, peak/mean intensity relative to the seasonal cycle, cumulative intensity (°C·day), and onset/decline rates. We also apply the widely adopted severity categorization introduced later (often referenced in 2018/2019 guidance), which bins daily anomalies by multiples of the exceedance scale Δ = thresh − seas into Moderate, Strong, Severe, and Extreme; these daily categories can be summarized per event and mapped across space and depth. This is exactly what we are preparing to visualize: daily fields (seas, thresh, anomalies, flags/IDs) and derived event statistics saved to NetCDF across all depths and, for domain runs, across the full grid. Computation is performed with the open-source Python package marineHeatWaves (GitHub link), which implements the Hobday algorithm and returns the climatology, threshold, daily diagnostics, and structured event tables used here. 

References
Hobday, A. J., et al. (2016). A hierarchical approach to defining marine heatwaves. Progress in Oceanography, 141, 227–238.
Hobday, A. J., et al. (2018). Categorizing and naming marine heatwaves. Oceanography, 31(2), 162–173.