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Floods set to worsen on Sumatra peat as landscape gives way

Fire fighters cooling burnt peatlands.

Fire fighters cooling burnt peatlands. Image courtesy of BPBD Riau.

  • A major flood at the turn of the year in Indonesia’s Riau province caused long-term traffic gridlock affecting thousands, with attendant knock-on effects for economic activity in the region.
  • One of Riau’s leading experts on peat hydrology told Mongabay that deterioration of the province’s carbon-rich peatland increases risks of disastrous flooding owing to reduced drainage, among other factors.
  • Indonesia’s peatland restoration agency said it had worked to rehabilitate 223,258 hectares (551,683 acres) of peat in Riau by end-2023, although large areas requiring urgent restoration work can’t be accessed because they’re located in private plantation concessions.

PEKANBARU, Indonesia — Traffic stopped gradually, then suddenly, as the new year approached around an hour’s drive out of the city of Pekanbaru here on the Indonesian island of Sumatra. Within minutes, the arterial highway linking the island’s east and west coasts turned into a dark river.

“The problem is complex,” said Sigit Sutikno, a peatland hydrologist at the University of Riau. “The floods will become more frequent, the impact will widen, and the duration will be longer.”

Across much of Indonesia’s Riau province, motorcyclists coated in translucent ponchos scrambled under shop awnings, while young children gazed out of car windows, unaware that the tailback snaked back for tens of kilometers.

Sigit said he expects extreme conditions like Riau’s New Year flood to worsen even without the aggravation of rainfall patterns caused by climate change, which will bring more frequent extreme weather events over Sumatra.

Dumai, a coastal city in Riau, is an area prone to forest and land fires.
Dumai, a coastal city in Riau, is prone to wildfires. Image courtesy of Walhi-Riau.

Thousands were caught up in the chaos on New Year’s Eve in Riau, which Sigit attributed to the deterioration of Indonesia’s largest peatland.

The province, which comprises much of Sumatra’s Malacca Strait coastline, accounts for a wider expanse of carbon-dense peatland than anywhere else in Indonesia. The country as a whole is home to around a third of the world’s tropical peat, which accumulates over thousands of years from the incomplete decomposition of plants in waterlogged marshes.

Peat accounts for about 3% of land surface area around the globe, but these dark marshes store more carbon than all other vegetation combined, according to the IUCN.

Around the 1980s, companies began cutting canals into millions of hectares of peat across Sumatra and Borneo to drain out the water in order to enable agriculture.

However, drying the peatland in this way has made swaths of Indonesia’s most carbon-rich ecosystems more prone to an array of disasters, like fire, floods and land subsidence.

Sigit monitors the health of this fragile landscape today as chair of the Center for Excellence in Peat Science and Technology and Disaster at the University of Riau. He and his colleagues have documented land subsidence rates of around 6 centimeters (2.4 inches) per year at a number of locations, such as Tanjung Leban village in the coastal district of Bengkalis.

There, he said, farming communities report the peatland in their gardens is running out. The thickness of the peat layer, which used to be 8 meters (26 feet), is now only around 2 m (6 ft). Researchers have installed stakes at 10 points around the village to measure the rate of subsidence.

Measuring peat subsidence can be done by checking the condition of coconut trees.
The height of the large mounds at the bases of coconut trees in the area are one indicator of peat subsidence. Image courtesy of Sigit Sutikno.

The structure of peat contains cavities that are ordinarily flooded when groundwater levels are maintained. However, when the peatland dries out, these pockets of space can’t support the load around them, causing the landscape to collapse in on itself.

“Subsidence during the dry season is higher than the rainy season,” Sigit said.

This process is exacerbated by actions that undermine the watershed, such as heat waves, forest clearing, and the cutting of canals by plantation companies to drain off water.

In recent years, local volunteers and Indonesia’s Peatland and Mangrove Restoration Agency, known by its Indonesian acronym BRGM, have worked to block many of these canals to keep the water from draining out — though Sigit said this offers only limited relief.

“That’s even if the construction of the canal barrier meets the standards and works both upstream and downstream,” he added.

Understanding the magnitude of peatland subsidence in Riau is complicated by extensive blind spots in the data. For example, Sigit and colleagues are often prevented from surveying land licensed to plantation companies.

“With companies, it’s difficult asking for permission,” he said.

An official measuring peat subsidence by calculating the age of the a coconut tree and the height of the roots that stick out to the ground surface.
A member of Sigit’s team measures the height of the above-ground roots of a coconut tree to see how far the peat has subsided. Image courtesy of Sigit Sutikno.

Recovery time

In 2015, President Joko Widodo established the BRGM, a dedicated agency under his direct authority, to restore peatlands in several priority provinces. The current target requires it to restore 1.2 million hectares (3 million acres) of peat by the end of this year.

By end-2023, data from the peat agency showed 816,235 hectares (about 2 million acres) of peatland had been restored, including 223,258 hectares (551,683 acres) in Riau.

“According to testimony from the community and local government, peat restoration facilitated by the BRGM can be said to have stopped forest and land fires in certain areas where they previously occurred every year,” Didy Wurjanto, an executive at the peat agency, told Mongabay Indonesia.

A new study published in May in the journal Scientific Reports found that construction of 257 small canal dams on 4,800 hectares (11,900 acres) of peatland in Sumatra both raised the water table and led to spontaneous tree growth.

However, problems remain in accessing corporate land and communicating the importance of rehabilitation work to some local communities growing plantation trees on peat.

“Intensive awareness raising and FPIC [free prior and informed consent] are needed as preconditions for peat restoration so that the benefits of restoration can be sustainable,” Didy said.

The flood at new year caused traffic problems between Riau and neighboring Jambi province for more than a month, jamming one of Sumatra’s most important supply chain routes.

“It’s complex — each impact creates a new impact,” Sigit said. “Sometimes I’m horrified when I tell stories like this. Riau, what will it be like in 30 years?”

Banner image: Firefighters cool off scorched peat in Sumatra. Image courtesy of BPBD Riau.

This story was reported by Mongabay’s Indonesia team and first published here on our Indonesian site on May 12, 2024.

As dry season looms, Sumatra villagers hope their peat restoration pays off


Hooijer, A., Vernimmen, R., Mulyadi, D., Triantomo, V., Hamdani, Lampela, M., … Swarup, S. (2024). Benefits of tropical peatland rewetting for subsidence reduction and forest regrowth: Results from a large-scale restoration trial. Scientific Reports14(1), 10721. doi:10.1038/s41598-024-60462-3

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