Correcting errors in the SPITFIRE fire model that result in excessively large and intense fires

The SPITFIRE fire model is used with several Dynamic Global Vegetation Models to model fire-vegetation interactions on a global scale. Since its development in 2010 it has been used for multiple studies in this field. The model consists of components that calculate ignitions, fire spread, post-fire mortality, and emissions. We find that the fire spread component of this model contains errors that introduce significant biases to its results. In particular, errors in the application of the Rothermel equation result in fires that are significantly too large and intense. Further, unphysically low live grass moistures in the model result in excessively fire-prone grasslands, and therefore a strong link between the presence of grasslands and the presence of fire. This combination results in areas where the SPITFIRE model calculates excessive tree mortality and consequent grassland formation. We perform a detailed analysis of these errors and examine the impact that corrections to them have on SPITFIRE model results.