[A-CG38] Climate Variability and Predictability on Subseasonal to Centennial Timescales

[ACG38-01] Seasonal predictability of mass coral bleaching events between the Pacific Ocean and the East China Sea with a large-ensemble climate model

*Takeshi Doi¹, Sayaka Yasunaka², Kurihara Haruko³ (1.JAMSTEC, 2.Tohoku University, 3.Ryukyu University)

Keywords:Large-ensemble seasonal prediction, Mass coral bleaching

In this study, we investigated the seasonal predictability of the Degree Heating Week, which is a widely used indicator to estimate thermal stress of corals and a strong predictor of coral bleaching, by the 108-ensemble-member seasonal prediction system for four seasons, March–May, June–August, September–November, and December–February, from the nine initialized dates (1st-9th) February, May, August, and November of 1982-2022. We found that the model is skillful in predicting the Degree Heating Week for most coral reef areas, including southern Japan during summer. We explored the origin of the success through the mixed-layer heat budget and statistical analyses, and found the contribution of La Niña and negative Indian Ocean Dipole events via the weakening of cooling by vertical diffusion induced by the low frequency of tropical cyclones in southern Japan. Successful prediction of the Degree Heating Week and also mass coral bleaching events in a season at least a few months in advance could help reduce the risk of coral reef collapse through necessary adaptation measures.