Abstract:
Tropical peatlands are a globally important carbon stock. They are being drained and deforested, resulting in large CO2 emissions. This CO2 flux depends on spatial and temporal patterns of drainage and land use. However, the extent of this subsidence remains controversial. Here, for the first time, we map subsidence rates across tropical peatlands in Southeast Asia using Interferometric Synthetic Aperture Radar (InSAR) remote sensing. The method allows us to monitor subsidence in remote locations, providing unprecedented spatial information, and the first comprehensive survey of land uses such as degraded peatlands, burnt and open areas, shrub lands, and smallholder farmlands. Strong spatial patterns emerged, with the highest subsidence rates occurring at the centers of peat domes, where the peat is thickest and drainage depths are likely to be largest. Peatland subsidence rates were also strongly dependent on current and historical land use. Based on millions of measurements, we characterize subsidence rates on drained peatlands. Scaling up these findings, we estimate average annual emissions of 156 Mt C/yr, and a possible range of 110-196 Mt CO2/yr due to peat decomposition in degraded peatlands across Southeast Asia.
