Assessing the Skill and Value of Seasonal Thermal Stress Forecasts for Coral Bleaching Risk in the Western Pacific

Over the last 30 years, coral reefs around the world have been under considerable stress because of increasing anthropogenic pressures, overfishing, pollution, and climate change. A primary stress factor is anomalously warm water events, which can cause mass coral bleaching and widespread reef damage. Forecasts of sea surface temperature (SST) and the associated risk of coral bleaching can assist managers, researchers, and other stakeholders in monitoring and managing coral reef resources. At the Australian Bureau of Meteorology, monthly forecasts of SST and thermal stress metrics have been developed that are based on a dynamical seasonal prediction system known as the Predictive Ocean Atmosphere Model for Australia (POAMA). To support the effective use of these forecasts in risk-based decision-making frameworks in the western and central tropical Pacific Ocean, the skill of these forecast tools in this region was assessed using several categorical forecast skill scores. It was found that the model provides SST forecasts with statistically significant skill up to 8 months in advance (correlation coefficient > 0.4; p=0.05) across the region. The highest skill (r>0.9) was achieved over the central equatorial Pacific Ocean, likely as a result of this region's strong relationship with the El Nino-Southern Oscillation (ENSO). Potential forecast value was assessed using a simplified cost-loss ratio decision model, which indicated that POAMA's seasonal hot-spot thermal stress forecasts can provide valuable information to reef management and policy makers in the western Pacific region.