Drainage Canals in Southeast Asian Peatlands Increase Carbon Emissions

Abstract

Drainage canals associated with logging and agriculture dry out organic soils in tropical peatlands, thereby threatening the viability of long‐term carbon stores due to increased emissions from decomposition, fire, and fluvial transport. In Southeast Asian peatlands, which have experienced decades of land use change, the exact extent and spatial distribution of drainage canals are unknown. This has prevented regional‐scale investigation of the relationships between drainage, land use, and carbon emissions. Here, we create the first regional map of drainage canals using high resolution satellite imagery and a convolutional neural network. We find that drainage is widespread—occurring in at least 65% of peatlands and across all land use types. Although previous estimates of peatland carbon emissions have relied on land use as a proxy for drainage, our maps show substantial variation in drainage density within land use types. Subsidence rates are 3.2 times larger in intensively drained areas than in non‐drained areas, highlighting the central role of drainage in mediating peat subsidence. Accounting for drainage canals was found to improve a subsidence prediction model by 30%, suggesting that canals contain information about subsidence not captured by land use alone. Thus, our data set can be used to improve subsidence and associated carbon emissions predictions in peatlands, and to target areas for hydrologic restoration.Tropical peatlands are swamp‐like environments in which naturally wet conditions slow the decomposition of plant carbon that would otherwise be released to the atmosphere. However, over the past few decades, humans have built drainage canals in Southeast Asian peatlands, due to economic pressure for logging and agriculture. These canals are a major threat to peatlands because they dry out peat soils, in turn speeding up decomposition and making soils susceptible to wildfire. Both of these mechanisms release massive amounts of carbon dioxide to the atmosphere, thereby accelerating climate change. Despite these risks, until now the extent of drainage in peatlands was unknown due to a lack of drainage canal maps. Here, we create the first regional map of drainage canals by training a computer algorithm to identify canals within high‐resolution satellite images. We find that drainage is widespread—occurring in at least 65% of Southeast Asian peatlands. Furthermore, we find that more drainage canals are related to progressively larger subsidence rates—deformations in the ground surface partly caused by carbon dioxide emissions to the atmosphere. These findings suggest that it is important to know where and how much drainage is occurring to accurately predict subsidence and target areas for restoration. We created the first map of drainage canals across Southeast Asian peatlands and find that they are present across 65% of the region There is substantial variation in drainage density within land use types, indicating that land use is an incomplete proxy for drainage Peat subsidence rates and associated carbon emissions are higher in areas with progressively more drainage canals