Marine Heatwave Category

The marine heatwave category scheme, defined by Hobday and colleagues in 2018, ranks the intensity of a marine heatwave by how far sea surface temperature exceeds the local 90th-percentile climatological threshold. A marine heatwave is a warm anomaly above that threshold lasting at least five days. Categories scale by multiples of the gap between the climatological mean and the 90th percentile: I Moderate (1 to 2 times), II Strong (2 to 3 times), III Severe (3 to 4 times), and IV Extreme (above 4 times). The thresholds are location and season specific, so the same absolute warming rates differently across regions.