The McArthur Forest Fire Danger Index (FFDI) used in Australia has a component representing fuel availability called the Drought Factor, which in turn is partly based on soil moisture deficit, commonly calculated as either the Keetch–Byram Drought Index (KBDI) or Mount’s Soil Dryness Index (SDI). The KBDI and SDI are essentially simplified water balance models to estimate soil moisture depletion in the upper soil levels, and are driven by precipitation and maximum temperature analyses.

In this study, we compare these two old empirical models against an emerging new approach in soil moisture estimation in the form of land surface modelling. Validation of these models is carried against in situ observations of soil moisture from OzNet and CosmOz networks in Australia. The results indicate that soil moisture from land surface model employed within the Bureau of Meteorology’s operational numerical weather prediction (NWP) model produce a more accurate estimation than KBDI and SDI. The average correlations obtained over all sites are 0.7, 0.58 and 0.67 for NWP, KBDI and SDI respectively. This study intends to be of a preliminary nature to the research that will be carried out to provide a better provision of soil dryness products with greater accuracy at a much higher spatial and temporal resolution for use in fire danger ratings.