GAMBUT field experiment of peatland wildfires in Sumatra: infrared measurements of smouldering spread rate

Abstract

Peatland wildfires present challenge to the mitigation of climate change due to the large amount of ancient carbon emission. Once ignited, the organic soils in peatland can burn for a long periods (weeks to months) and are difficult to extinguish. Peat fire is governed by smouldering combustion which is the slow, low temperature, flameless burning of charring porous fuel, and the most persistent type of combustion phenomena. The detection and monitoring of peatland wildfires are often conducted by remote sensing like satellite. However, there is currently a missing gap between spread of peat fires in the small laboratory scale and the large field scale. This work covers this gap by conducting field-scale controlled experiment of peatland wildfires. The experimental campaign, GAMBUT, was conducted in the peatland of Sumatra, Indonesia, covering an area of 374 m2. Smouldering spread rate was measured by infrared cameras and subsurface thermocouples. The smouldering sustained up to 10 days and nights, and survived against three rainfalls. Observation from infrared images show that horizontal smouldering spread rate fluctuates during propagation. However, no significant difference was found between average horizontal spread rates from the measurements of infrared camera and thermocouples, i.e. 0.3±0.13 cm/h to 0.8±0.2 cm/h. The spread rates here agree with the trend in the literature of laboratory experiments, fit within in the ranges of high moisture (MC) and inorganic (IC) contents of the soil (MC between 23 to 141% and IC between 49 to 72%). Even though slower, the fires thrived up to 10 days and against three rainfalls, demonstrating the persistency of smouldering peat fires and calling for a consideration of degraded peatland with high inorganic content to be consistently included in the mapping and monitoring of peatland area. GAMBUT presents a unique understanding of peatland wildfires at field conditions and aims to contribute to the better monitoring and mitigation acts.