3D modeling of coupled soil heat and moisture transport beneath a surface fire

Understanding the soil heat and moisture transport is significant for assessing the living condition of vegetation and microorganisms in soils. Numerous studies have been conducted to understand the coupled soil heat and moisture transport under normal environmental conditions; while this coupled transport under extremely high-temperature conditions caused by surface wildfires is little understood. Particularly, 3D modeling of such coupled transport is absent. Here, we develop a 3D model to understand more realistic characteristics of the soil heat and moisture transport beneath a surface fire. With the 3D model, we investigate the lateral transport of soil heat and moisture in a 3D space, the influence of a surface fire on soil moisture and temperature conditions in neighboring regions without fires, and the effect of initial water contents on the delay of soil heating. The modeling results showed that the lateral transport leads to an obvious difference in soil temperature and moisture between the inside and border area of the fire region. Such a difference cannot be considered with a 1D model widely used in existing studies. For the initial water content effect, we confirmed that a high initial water content delays the soil heating to cooler regions at deeper soil depths during the late stage of soil heating. Our results also showed that a surface fire significantly changes soil heat and moisture in the no-fire region neighboring to the simulated fire. At the location 50 m away from the fire region, the soil temperature and moisture in upper soil layers can increase to over 85 degrees C and decrease to 0.006 m(3) m(-3) within 5 h, respectively. This study provides important insights, which are useful for fire management but have not been reported before, for understanding more physically realistic characteristics of the 3D soil heat and moisture transport beneath a surface fire in both the fire and no-fire regions. (C) 2019 Elsevier Ltd. All rights reserved.