The dispersion of smoke haze from peatland fires over South Sumatra during the moderate El Niño of 2023

Fires in peat forests do not occur suddenly but are preceded by a slow decline in the Groundwater Level (GWL) below its critical depth. Typically, a few weeks later, multiple fires start to emerge, primarily resulting from human activities. This paper investigates the occurrence of peatland fires in South Sumatra at the end of September 2023 (during a moderate El Niño event) when the smoke haze dispersed into the city of Palembang (the capital city of South Sumatra), leading to a decrease in ground visibility of approximately 250 m. We utilize GWL data measured in peatlands and determine the critical depth using the modified Keetch-Byram index (mKBDI). Equipped with low-cost sensors and employing mathematical models, we examine the dispersion behavior of smoke haze. The source of the fires was identified using FIRMS data, revealing that the majority of fire spots were situated in peatlands to the south of the city of Palembang. Our findings indicate that observed PM_2.5 concentrations exhibit a diurnal cycle pattern, peaking at morning and reaching their minimum at evening. We propose using a modified Ermak model instead of the Gaussian model to quantify haze dispersion, which demonstrates results in good agreement with satellite observations. We suggest that preserving the southern region of the South Sumatra province as a peat swamp forest is an effective way to mitigate the impending haze disaster facing the city of Palembang.