Overview
In late November 2025, rare tropical Cyclone Senyar dumped extreme rainfall on Indonesia’s Sumatra island, unleashing catastrophic floods and landslides across the provinces of Aceh, North Sumatra and West Sumatra. By December 6, Indonesian authorities reported at least 900–916 deaths and hundreds missing, with more than 3 million residents affected and around 1 million displaced across 50 regencies. The same storm systems killed roughly 200 more people in southern Thailand and Malaysia, turning a regional weather anomaly into a multi-country disaster.
As rescuers struggle through debris-choked valleys and survivors in places like Aceh Tamiang walk over piles of felled logs to reach volunteer aid centres, attention has shifted from the storm itself to what made it so deadly. Environmental groups and local communities point to years of deforestation, mining, logging, palm oil expansion and large infrastructure projects in the Batang Toru and other river basins, arguing that these activities stripped hillsides of forest, accelerated erosion and turned heavy rain into lethal flash floods. In response, Jakarta has opened investigations into at least 12 companies, suspended operations in the Batang Toru basin pending environmental audits, and pledged to revoke permits where violations are proven—while President Prabowo Subianto faces pressure to formally declare a national disaster and to treat this as a turning point for Indonesia’s land-use and climate policy.
Key Indicators
People Involved
Organizations Involved
The central government of the Republic of Indonesia, responsible for national disaster policy, environmental regulation and coordination with provincial authorities.
Indonesia’s BNPB is the central agency responsible for disaster risk reduction, emergency response and coordination with provincial disaster offices.
WALHI, Friends of the Earth Indonesia, is the country’s largest environmental network, active on issues from deforestation and mining to climate justice.
JATAM is an Indonesian network focusing on the social and environmental impacts of mining and energy projects.
NSHE is the consortium developing the controversial Batang Toru hydropower plant in North Sumatra, a project linked to China’s Belt and Road Initiative.
Timeline
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Death toll in Sumatra floods surpasses 900 as Batang Toru firms suspended
Government ActionOn December 6, Indonesian authorities report that the death toll from cyclone-induced floods and landslides across three Sumatran provinces has risen to around 908–916, with 270–410 people still missing. Survivors in Aceh Tamiang recount walking for an hour over slippery logs and overturned cars to reach volunteer-run aid centres. Environmental groups continue to blame deforestation from mining, logging and infrastructure projects for worsening the disaster. The environment ministry orders all companies in the Batang Toru River Basin and nearby Garoga basin to halt operations for environmental audits, summoning three firms to Jakarta for inspection on December 8. Calls intensify for President Prabowo to declare a national disaster, but he maintains that existing arrangements are sufficient for now.
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Authorities trace origin of massive log flows
InvestigationFollowing meetings with the national police chief, Forestry Minister Raja Juli Antoni says investigators are tracing the origin of logs swept away by floods, examining links to illegal logging, oil-palm and mining land clearing, and various land rights schemes. The statement underscores the possibility of both legal and illegal land-use practices contributing to the disaster.
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Government identifies 12 suspect firms; vows action on mining permits
InvestigationForestry Minister Raja Juli Antoni tells parliament that authorities have identified 12 companies suspected of contributing to the floods and landslides through illegal or excessive forest clearing, many in the Batang Toru region. Separately, Investment and energy officials say they will revoke mining permits for companies found in violation, while environmental watchdogs highlight some 54,000 hectares of forest converted for extraction in affected areas. BNPB updates the toll to 836 dead and 517 missing.
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Prabowo orders national-level response but stops short of national disaster status
Government ActionPresident Prabowo Subianto instructs that the Sumatra floods and landslides be treated as a national priority, ordering ministries, the military and police to fully mobilise resources. Officials clarify that while the response is at a national level, the disaster has not yet been formally designated a "national disaster" under Indonesian law, prompting continued calls from local leaders for an upgrade to unlock additional relief funds.
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Locals and officials blame ‘mischievous hands’ and deforestation
Public BacklashIn a widely cited Reuters report, residents and officials in North Sumatra describe logs littering beaches and rivers and accuse logging, mining and palm oil companies of exacerbating the disaster through rampant deforestation. Environmental groups say Sumatra has lost 4.4 million hectares of forest since 2001, and that projects like the Batang Toru hydropower plant and the Martabe gold mine have degraded ecosystems and increased landslide risk.
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Batang Toru region hit by debris-laden flash floods
Disaster ImpactFlash floods in the Batang Toru area of South Tapanuli send heavy machinery and large volumes of logs downstream, with images of log-jammed rivers and destroyed infrastructure going viral and fuelling speculation about illegal logging and construction waste.
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WALHI names seven companies behind ecological damage
NGO StatementWALHI North Sumatra publicly accuses seven companies—including PT Agincourt Resources, PT North Sumatra Hydro Energy and PT Toba Pulp Lestari—of deforestation, river alteration and wildlife corridor destruction in the Batang Toru basin, arguing that this ecological damage magnified the impact of Cyclone Senyar-induced floods and landslides.
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Early flood tolls in Sumatra surpass 170 dead
Disaster ImpactBy November 28, Indonesia’s disaster agency reports at least 174 dead and 79 missing from flash floods and landslides on Sumatra, with North Sumatra, Aceh and West Sumatra hardest hit. Thousands of homes are submerged, roads and bridges collapse, and tens of thousands flee to temporary shelters.
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Cyclone Senyar forms and makes landfall near Sumatra
Meteorological EventCyclonic Storm Senyar develops over the Strait of Malacca and makes landfall on northeastern Sumatra around November 25–26, bringing extreme rainfall that sets the stage for widespread floods and landslides across Aceh, North Sumatra and West Sumatra, as well as southern Thailand and Peninsular Malaysia.
Scenarios
Targeted sanctions and symbolic reforms, but business largely as usual
Discussed by: Analysts and reporting in Reuters, Antara and Indonesian media highlighting permit reviews but cautious about deep structural change
Under this scenario, the government maintains intense rhetoric but confines action to a limited set of highly visible companies, especially those already controversial like NSHE and Agincourt Resources. A handful of permits are suspended or revoked, some executives face administrative sanctions, and selected restoration projects are announced in Batang Toru and high-profile watersheds. However, large-scale forest clearing for plantations, mining and infrastructure continues under slightly tighter procedural rules. Prabowo’s administration frames the response as balancing economic growth with environmental responsibility, and the immediate political crisis passes once casualty figures stabilise and aid flows normalise. The underlying drivers—fragmented land governance, permissive licensing and weak enforcement—remain largely intact, making a similar disaster likely in future La Niña years.
Precedent-setting crackdown and legal cases reshape land-use politics
Discussed by: Environmental NGOs like WALHI and JATAM, some legal scholars and climate advocates pushing for a ‘Sumatra moment’ akin to past watershed court rulings
Here, the scale of the tragedy and clear evidence of deforestation push Prabowo’s government, courts and prosecutors into unusually forceful action. Environmental audits in Batang Toru and other basins lead to revocation of multiple mining, plantation and infrastructure permits, including for politically connected firms. Class-action or public interest lawsuits seek damages and ecosystem restoration orders, and the Constitutional Court or Supreme Court issues decisions tightening standards for Environmental Impact Assessments and disaster risk in land-use planning. Indonesia uses the crisis to bolster its climate diplomacy—highlighting loss and damage—while also tightening domestic green taxonomy rules so that hydropower and other projects in high-risk, biodiverse areas face stricter scrutiny or are cancelled. This scenario would mark a structural shift in how climate risk and cumulative impacts are integrated into permits, but requires sustained political will that has often been absent in past disasters.
Scapegoating a few firms while systemic deforestation quietly continues
Discussed by: Skeptical NGO voices and some independent commentators noting Indonesia’s long history of post-disaster blame without structural reform
In this outcome, investigations focus heavily on a narrow set of companies—perhaps those already unpopular or financially weak—while other powerful operators and underlying permitting practices escape serious scrutiny. A few firms in Batang Toru are punished and used as examples, but no comprehensive review of land concessions, peatland drainage, or forest-zoning policy occurs. Government narratives increasingly stress the ‘unprecedented’ nature of Cyclone Senyar and global climate change rather than domestic governance failures. Over time, public attention fades, development projects resume after cosmetic adjustments, and local communities remain exposed to similar compound risks of extreme rainfall, unstable slopes and sediment-choked rivers.
National disaster designation triggers broader climate adaptation push
Discussed by: Disaster management experts, some legislators and regional leaders calling for stronger central coordination and funding
If casualty numbers and humanitarian needs continue to rise, Prabowo may formally declare the Sumatra floods a national disaster. This would unlock additional budgetary and operational tools, justify large-scale relocation or rebuilding programs, and open the door to new climate adaptation finance from multilateral banks and partners. In an ambitious version of this path, the government uses post-disaster reconstruction to pilot river-basin-based land-use planning, stricter setback zones, and community early-warning systems, while integrating climate projections into infrastructure design. However, this would require overcoming resistance from local elites and industries that benefit from current patterns of land exploitation. The balance between immediate relief politics and long-term adaptation planning will determine how far this scenario goes beyond rhetoric.
Historical Context
2021 South Kalimantan floods tied to palm oil and coal mining
January 2021What Happened
In early 2021, Indonesia’s South Kalimantan province experienced severe flooding that displaced hundreds of thousands of people. Environmental groups and investigative outlets found that large areas of forest and peatland had been converted for oil palm plantations and coal mining, with data showing that mining and plantation concessions covered around half of the province’s land area. Analysts argued that this land-use change worsened runoff and reduced the landscape’s capacity to absorb heavy rain, making the floods more destructive than they would otherwise have been.
Outcome
Short term: The government provided emergency relief and some officials promised tighter oversight, but no sweeping reforms to mining or plantation licensing followed immediately.
Long term: South Kalimantan became a reference case for how extractive industries and monoculture plantations can amplify hydrometeorological disasters, informing later critiques of land-use practices in events like the 2025 Sumatra floods.
Why It's Relevant
The South Kalimantan floods show how the combination of legal concessions and weak enforcement can prime a landscape for catastrophe when intense rainfall occurs—a dynamic now strongly echoed in Sumatra, where mining, hydropower and plantation concessions intersect with steep terrain and high biodiversity.
2013 Uttarakhand floods and India’s hydropower reckoning
June 2013 – mid-2010sWhat Happened
In June 2013, unprecedented rainfall triggered catastrophic floods and landslides in India’s Himalayan state of Uttarakhand, killing thousands and devastating the pilgrimage town of Kedarnath. Subsequent inquiries and court cases examined the role of numerous hydropower projects and road construction in destabilising slopes and altering river systems. In a landmark admission to India’s Supreme Court, the central environment ministry acknowledged that hydropower projects had aggravated the disaster, noting that maximum damage sites were located upstream or downstream of these projects and that ecological degradation and non-compliance had enhanced landslide and flood impacts.
Outcome
Short term: The Supreme Court halted dozens of planned hydropower projects, and some existing projects faced tighter scrutiny and mitigation requirements.
Long term: Uttarakhand’s experience helped entrench the principle that cumulative impacts and disaster risk must be factored into river-basin planning, although implementation has been uneven and development pressure remains high.
Why It's Relevant
The Uttarakhand case offers a precedent for how courts and regulators might treat claims that hydropower, mining and road projects worsened the Sumatra floods, especially in the Batang Toru basin where similar concerns about slope stability, deforestation and seismic risk have been raised.
2018 Kerala floods and ecological warnings on land-use
August 2018 – early 2020sWhat Happened
In 2018, the Indian state of Kerala suffered devastating floods after receiving some of the heaviest rainfall in a century. Post-disaster studies found that ecological degradation—such as deforestation, harmful land use in upland areas, quarrying, and sand mining in river channels—had contributed to topsoil loss, siltation and reduced water absorption capacity. Water researchers argued that the stripping of topsoil to depths of up to two metres in some upland regions fundamentally weakened the landscape’s ability to buffer extreme rainfall, exacerbating floods and leading to drought-like conditions soon afterward as water rapidly drained away.
Outcome
Short term: Kerala launched reconstruction efforts and commissioned studies into land-use and ecological drivers of the floods, but controversial quarrying and development continued in many areas.
Long term: The floods intensified debate in India over how climate change interacts with land-use decisions, reinforcing calls for landscape-level planning that integrates ecology, disaster risk and development—debates that parallel Indonesia’s current discussions after the Sumatra floods.
Why It's Relevant
Kerala’s experience underscores that extreme rainfall events like Cyclone Senyar’s downpours in Sumatra become disasters partly because of how landscapes are managed. It strengthens the argument made by Indonesian scientists and NGOs that deforestation, quarrying, and river alteration in Sumatra have turned heavy rain into mass-casualty events.