Most of that choking haze that engulfs South-East Asia annually comes from peatland catching fire during the dry season in the middle of the year. Not only is the smoke a huge health hazard but the fires also increase emissions of greenhouse gases across South-East Asia.
Peatland is wet and soggy in its natural state; once it dries out, it becomes highly flammable. Dry peatland, once set alight to clear it of vegetation, can burn for days or weeks, even smouldering unseen underground after the fire above has been extinguished.
Peatland is also considered to be one of the most efficient carbon sinks so burning it releases all that sequestered carbon dioxide into the air.
The problem is, more and more peatland in South-East Asia is drying out, sinking, and becoming a fire hazard because it is being drained.
One research team found that draining for agriculture is causing peatland in the region to sink by an average of 2.24cm a year. Researchers from the Singapore-Massachusetts Institute of Technology Alliance for Research and Technology (SMART) discovered that 90% of the peatland they studied sank at this rate between 2007 and 2011.
The results of their study – which used satellite mapping through the InSAR remote sensing radar technique – was recently published in an article titled “Widespread Subsidence and Carbon Emissions Across South-East Asian Peatlands” in Nature Geoscience, a monthly, peer-reviewed scientific journal.
The researchers warn that the region is now facing loss of productive land and flooding as well as saltwater intrusion because much of the peatland is now near sea level, which is too low.
Previously, most studies used poles anchored in the peatland to document the change and were mainly focused on large scale plantations. However, SMART’s study shows that the subsidence is not limited to plantations.
“Our measurements reveal that smallholder agricultural areas and degraded peatlands are subsiding at rates comparable to those of plantations, and that subsidence rates increase away from rivers, ” it states.
Plantations account for only 27% of the subsidence while the rest is due to drainage for, among others, smallholder agriculture, creating canals to float out timber, digging ditches, and preparing land for large-scale rice farming experiments.
South-East Asia has around 60% of the world’s tropical peatland, including what is thought to be the oldest, at around 47,800 years, in Putussibau, Indonesia.
Malaysia has some 2.5 million hectares of peatland, making up about 7.5% of the country’s land area; of this, almost 70% is found in Sarawak, amounting to 1.7 million hectares. Peatland in Malaysia is the most widespread type of wetlands.
With their unique InSAR (Interferometric Synthetic Aperture Radar) technique, the researchers used satellite data to detect changes in the surface elevation of some 2.7 million hectares, making up 10% of peatland located mostly along coastal regions in south-western Sarawak and parts of Indonesia, like Sumatra and Kalimantan (see map).
Even if it doesn’t catch fire, drained peatland that dries out releases CO2 into the atmosphere, sinking as the sequestered carbon escapes.
Peatland comprises partially decayed vegetation and organic matter and is formed in wet conditions when flooding or stagnant water obstructs the flow of oxygen and slows down the rate of decomposition (see graphic).
Charles Harvey, principal investigator at SMART, and a professor at MIT’s Department of Civil and Environmental Engineering, explains in an email interview that drainage lowers the water table, allowing oxygen to enter the peatland.
“The oxygen is consumed by microbes that convert the organic carbon that composes peatland into carbon dioxide.”
Subsidence is caused by the transformation of solid peatland into carbon dioxide: “Subsidence and carbon emissions are the same – the peatland becomes carbon dioxide emissions.
“The land surface drops because the peat has been converted into carbon dioxide, a gas that leaks into the atmosphere. This process is caused by drainage.”
The SMART study, says Prof Harvey, confirms that peatland oxidation is a large source of CO2 emissions in South-East Asia.
The study contends that large amounts of organic carbon stock within tropical peatland was being emitted as CO2 at a rate of 132 to 159 million tonnes of carbon per year in 2015 (estimated on the basis of the Intergovernmental Panel on Climate Change emission factors).
“Regional carbon dioxide emissions from peatland loss during a typical year contributes significantly to carbon emissions from Indonesia and Malaysia, ” says Prof Harvey.
“These emissions from peatlands can surpass regional fossil fuel emissions during particularly dry years when there are widespread peat fires, ” he adds.
His team’s study shows that while the damage is occurring across almost all the peatland they surveyed, the worst may be in the Mega Rice Project area in Kalimantan and “also very bad areas in Sumatra”.
According to economist.com, the Mega Rice Project was initiated in 1995 to convert 10,000sq km into padi fields but failed, because peatland isn’t conducive to padi cultivation, and was halted in 1999.
Current Indonesian President Joko Widodo has greenlighted a 1,650sq km agriculture zone in the same area.
Large source of carbon
Supporting the findings of the SMART study, Malaysia-based Global Environment Centre director Faizal Parish says the 2.24cm sink rate is only the average and that actual subsidence rates may be even higher in some areas.
“For drained peatlands, especially on plantations, the subsidence rate may be 5cm a year or more.
“At 5cm a year subsidence, that will be 1m of subsidence over one cycle of oil palm cultivation on peatland, which is about 20 years, ” says Faizal in an email interview (he was not involved in the SMART study).
In West Johor, for example, over 4m of subsidence has been recorded following extensive drainage during the 1970s, he says.
“This has led to massive problems of flooding, collapse of infrastructure, exposure of acid sulphate soils, acidification of groundwater, saline intrusion and more.”
Faizal is also worried about the serious short- and medium-term risk of drained peatland eventually becoming unusable and abandoned.
“The high greenhouse gas emissions from degrading peatland is also one of the largest sources of emissions in Malaysia and needs to be seriously addressed if we are to meet the targets for emission reduction under our Nationally Determined Contributions, ” adds Faizal.
Malaysia’s target is to reduce greenhouse gas emission intensity by 40% by 2030.
Nevertheless, all is not lost – yet.
Both Prof Harvey and Faizal think that it is still possible to at least slow down – or even reverse in some areas – the drainage and subsistence process and, hence, reduce the magnitude of fires we have come to expect during the “haze season” between July and September every year.
“It is possible to slow down the subsidence rate through good water management and, at appropriate sites, restoration of forest cover can lead to a reversal of subsidence if we are successful in restoring fully the peatland ecosystem and enabling new peat formation, ” says Faizal.
He warns, though, that such a process takes time and will not be successful in many areas. It is also expensive.
“For badly degraded sites, it will take thousands of years to recover considering that the growth of new peat may only be at the rate of 1mm a year, ” he points out.
Faizal estimates that this means it will take between 25 and 50 years to repair the damage caused by one year of drainage.
Better control of when and where drainage takes place would reduce the problem, agrees Prof Harvey.
“The water table remains closer to the surface, preventing fires, if peatland is not drained. Under natural undrained conditions, the water table rarely falls so low that the peat becomes flammable.
“This is why peat accumulated for thousands of years without burning but is now burning after being drained.”
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