Closing the gap between lab and field: An exploration of fire experiments across scales

A large challenge in predictive wildfire science arises from working at the intersection of many processes and scales controlling wildfire behavior. Two main scale differences arise in prescribed field and laboratory burn experiments. Prescribed field burns are one of many areas of wildfire research where scaling mismatches often arise due to the heterogeneities that exist in natural environments and the locations and size of these experiments often align with management needs. Laboratory fire experiments have long been used to characterize prescribed fire behavior and inform policy decisions and weigh legal considerations. Extrapolating fire behavior from the laboratory to the field scale is difficult due to scaling mismatches and the possibility of new physical processes dominating at the field scale. In this work, we compare fire measurements between the laboratory and the field and contextualize the differences from physical and ecological perspectives. To that end, temperature-time curves are utilized as potential metrics for characterizing differences in fire behavior across scales. It is found that while fire rate of spread and flame temperature are similar, fireline intensity is significantly different between laboratory and field environments. It is also found that a majority of measured fires are heading fires, necessitating a higher volume of backing fire experiments. The inability to maintain 4 dimensionless groups (Reynolds number, Froude number, Buoyancy number, Byrams energy criterion) across scales is suggested as an explanation for the mismatch in fireline intensity. We discuss the implications of these results on the semi-empirical Rothermel model.