Impact of Land Use Change and Drought on the Net Emissions of Carbon Dioxide and Methane From Tropical Peatlands in Southeast Asia

Abstract Peat decomposition is progressing in Southeast Asia due to lowered groundwater levels (GWL) caused by drainage. Additionally, droughts during El Niño events significantly lower the GWL, the main environmental factor that controls greenhouse gas (GHG; carbon dioxide (CO 2 ) and methane) emissions in peatlands. Consequently, tropical peatlands have been recognized as a significant source of carbon emissions, and these emissions have been estimated for the region using constant decomposition rates of peat for each land use (Tier 1 emission factors). However, these factors hardly reflect the spatiotemporal variation of the GWL. Furthermore, these estimates do not account for CO 2 uptake through photosynthesis. To reduce uncertainty, we developed a method to estimate spatiotemporal GWL variation from satellite‐derived antecedent precipitation. Using the estimated GWL, we calculated the monthly net ecosystem‐scale GHG emissions from peat forests and managed peatlands using the observed relationship between eddy covariance GHG fluxes and GWL, though carbon losses from deforestation, fires, and fluvial export were not covered in this study. Spatiotemporal variations in GHG emissions across Sumatra, Borneo, and the Malay Peninsula over a decade revealed the following: (a) Peat forests are a net source of CO 2 ‐equivalent GHGs, even when undrained, (b) Decadal mean annual GHG emission rates increase 2.8‐fold when forests are drained and 6.4‐fold when undrained forests are converted to managed peatlands, (c) Droughts increase total annual GHG emissions by 16% across the study area. Additionally, climate models projected precipitation increase in the mid‐21st century, suggesting an increase in GWL and a consequent reduction in peat decomposition.