The Community Fire Behavior Model for coupled fire-atmosphere modeling: Implementation in the Unified Forecast System

Abstract. There is an increasing need for simulating the evolution of wildland fires. The realism of the simulation increases by accounting for feedbacks between the fire and the atmosphere. These coupled models combine a fire behavior model with a regional numerical weather prediction model and have been used for fire research during the last decades. This is the case, for instance, of the state-of-the-art Weather Research and Forecasting model with fire extensions (WRF-Fire). Typically, the coupling includes specific code for the particular models being coupled such as interpolation procedures to pass variables from the atmospheric grid to the fire grid, and vice versa. However, having a fire modeling framework that can be coupled to different atmospheric models is advantageous to foster collaborations and joint developments. With this aim, we have created, for the first time, a fire behavior model that can be connected to other atmospheric models without the need of developing specific low-level procedures for the particular atmospheric model being used. The fire behavior model, referred to as the Community Fire Behavior model (CFBM), closely follows WRF-Fire version 4.3.3 methods in its version 0.2.0, and makes use of the Earth System Modeling Framework library to communicate information between the fire and the atmosphere. The CFBM can be also run offline using an existing WRF simulation in what we refer to as the standalone model. Herein we describe the fire modeling framework and its implementation in the Unified Forecast System (UFS). Simulations of the Cameron Peak Fire performed with UFS and WRF-Fire are presented to verify our implementation. Results from both models, as well as with the standalone version, are consistent indicating a proper development of the CFBM and its coupling to the UFS-Atmosphere. These results, and the possibility of using the fire behavior model with other atmospheric models, provide an attractive collaborative framework to further improve the realism of the model in order to meet the growing demand for accurate wildland fire simulations.