Fire weather simulation skill by the Weather Research and Forecasting (WRF) model over southeast Australia.

The fire weather of southeast Australia from 1985-2009 has been simulated using the Weather Research and Forecasting (WRF) model. The U.S. National Oceanic and Atmospheric Administration Centers for Environmental Prediction / National Center for Atmospheric Research reanalysis supplied the lateral boundary conditions and initial conditions. The model simulated climate and the reanalysis were evaluated against station-based observations of the McArthur Forest Fire Danger Index (FFDI) using probability density function skill scores, annual cumulative FFDI and days per year with FFDI above 50. WRF simulated the main features of the FFDI distribution and its spatial variation, with an overall positive bias. Errors in average FFDI were caused mostly by errors in the ability of WRF to simulate relative humidity. In contrast, errors at extreme FFDI values were driven mainly by WRF errors in wind speed simulation. However, in both cases the quality of the observed data is difficult to ascertain. WRF run with 50 km grid spacing did not consistently improve upon the reanalysis statistics. Decreasing the grid spacing to 10 km lead to fire weather that was generally closer to observations than the reanalysis across the full range of evaluation metrics used here. This suggests it is a very useful tool for modelling fire weather over the entire landscape of southeast Australia.

Figure 9: WRF 10 km map of mean annual cumulative FFDI (1985–2009). Markers show observed values. Small black markers show examples of places where days per year with FFDI over 50 differs substantially from the surrounding area.