Characterizing and predicting smoldering temperature variations based on non-linear mixed effects models

Underground fires are slow spreading, long-lasting and low temperature smoldering combustion without flames, mainly occurring in peatlands and wetlands with rich organic matter. The spread of the smoldering is maintained by heat released during combustion and monitoring this is an important approach to detect underground fires. The Daxing’an Mountains region is a hotspot for underground fires in northeast China. This study examined a Larix gmelinii plantation in the Tatou wetlands of the Daxing’an Mountains and determined the maximum temperature variation of humus of varying particle sizes, and the temperature rising process based on non-linear mixed effects models by an indoor combustion experiment. Maximum combustion temperatures up to 897.5 °C, increased with humus depth; among the three models tested, Richard’s equations were best for characterizing temperature variations; a non-linear equation with three parameters had the highest accuracy in fitting the combustion temperature variations with varying humus particle sizes. These results are informative for predicting temperature variations and provide technical support for underground fire monitoring.