Subseasonal drivers of extreme fire weather in Australia and its prediction in ACCESS-S1 during spring and summer

Subseasonal drivers of extreme fire weather in Australia and its prediction in ACCESS-S1 during spring and summer

We assess the ability of the Bureau of Meteorology’s ACCESS-S1 dynamical forecast system to simulate and predict extreme fire weather over Australia during austral spring (SON) and summer (DJF) on subseasonal timescales. Specifically, we focus on the roles of the El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), Southern Annular Mode (SAM), Madden–Julian Oscillation (MJO), and two modes of persistent high-pressure in the Australian region characterised as (i) split-flow blocking highs and (ii) subtropical ridge Tasman highs (STRH). The observed likelihood of extreme fire weather increases over most of Australia in association with El Niño, the positive IOD, negative SAM and low split-flow blocking, in both seasons. These increases are generally largest in SON over the southeast. Notable increases in the likelihood of extreme fire weather also occur north of 30° S during low STRH activity, and over the southeast during MJO phase 3. Using retrospective forecasts at lead times of 2–3 weeks for the period 1990–2012, we show that ACCESS-S1 simulates reasonably well the observed modulation of extreme weekly-mean fire weather by each climate driver, however the simulated changes in probabilities are often weaker than those observed. Each climate driver plays an important role in providing predictive skill for regions where ACCESS-S1 captures a high likelihood of experiencing extreme fire weather conditions. The results of this study highlight windows of forecast opportunity during active climate driver phases that can be useful to regional users in fire management, emergency services, health, national park management, and the agriculture and energy sectors.