Mapping carbon dioxide (CO₂) emissions from peat subsidence using carbon parameters and InSAR observations in South Kalimantan, Indonesia

Peatlands are recognized as one of the largest terrestrial carbon sinks and are pivotal in efforts to mitigate climate change. Given this, Indonesia has committed to managing its peatlands, which have been subjected to drainage, deforestation, fires, and conversion for development. As of 2015, the Center for Agricultural Land Resources has mapped 107,344 ha of peatlands in South Kalimantan Province. However, in 2019, forest fires destroyed 2,400 ha of land, leading to the decomposition of surface peat areas, land subsidence, and the release of carbon into the atmosphere as CO₂. This study aimed to quantify the widespread loss of peat carbon using the PS-InSAR (Persistent Scatterer Interferometric Synthetic Aperture Radar) technique. Specifically, 66 Sentinel 1 SAR images of SLC were used to map subsidence in the peatland area between January 2019 and January 2021. The carbon content and bulk density of peatland were then quantified to estimate CO₂ emission. The results obtained through the PS-InSAR technique showed that the highest level of peat subsidence was at –50 mm year^–1 in the Landasan Ulin Sub–district of Banjarbaru Regency. Furthermore, subsidence was identified in 6,920.5 ha of peatland in the study area. Subsidence, peat area, and carbon content data from SAR images, optical images, and peat soils were gathered through field surveys and websites (GSOCMap and Zenodo) to estimate CO₂ emission. The estimated CO₂ emissions based on in–situ and website data were the highest at 0.29 t C ha^–1 year^–1 and 0.04 t C ha^–1 year^–1 in Beruntung Baru Sub-district, Banjar Regency, and Bumi Makmur Sub-district, Tanah Laut Regency, respectively.