ACCESS-MICAS: A Forecast-Based Tool for Event Attribution and Projection

Le résumé fourni par la source

Abstract The Australian Community Climate and Earth-System Simulator–Modified Initial Condition Attribution System (ACCESS-MICAS) is a forecast-based numerical modeling tool used to understand the causes of multiday to seasonal climate events by altering states in the forecast initial conditions and forcing. Built on the Bureau of Meteorology’s operational global coupled subseasonal to seasonal forecast system, ACCESS-S2, we reforecast an event with hypothetical atmosphere, land, and ocean initial conditions and/or external forcings. The system is primarily designed to assess the potential contribution of anthropogenic climate change to the magnitude of a weather event or climate extreme but can be applied more generally to assess the sources of predictability or response to an imposed anomaly. This paper describes the system with a specific focus on the climate change attribution configuration. We examine key technical aspects, including the required spinup time, the presence of initialization shock, and the model’s ability to represent an altered climate, including dynamical changes. The system is applied to the 2019–20 Australian Black Summer, focusing on the role of ocean state in modulating temperature and rainfall and the influence of anthropogenic climate change on heat wave intensity and fire weather conditions. Results show that the positive Indian Ocean dipole increased the temperature and suppressed rainfall in northwest Australia, exaggerating the fire danger in the region, while climate change contributed significantly to the severity of heat extremes and fire danger, with the event being even more extreme in the future climate. These results demonstrate the utility of ACCESS-MICAS for both attribution and broader climate diagnostics.

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