Cyclone Senyar Landslide Kills 7 Percent of Tapanuli Orangutans

TEMPO.CO, Jakarta – About seven percent of the critically endangered Tapanuli orangutan population is believed to have disappeared due to one extreme weather event. This finding is the main focus of a study published in the journal Current Biology, which analyzed the impact of Cyclone Senyar on Tapanuli orangutans in Indonesia.

Based on official statements from Borneo Futures and World Weather Attribution, researchers found that extreme rainfall from Cyclone Senyar in November 2025 triggered a landslide in the western block of the Batang Toru ecosystem, the area that is the largest habitat of the remaining Tapanuli orangutan population. The scientific team analyzed the landslide's traces recorded through satellite images and combined them with estimates of orangutan density in the area.

The analysis results indicate that about 58 Tapanuli orangutans are estimated to have died as a result of the landslide. This number is equivalent to about 11 percent of the Tapanuli orangutan population in the West Block of Batang Toru, or about 7 percent of the remaining population in the wild.

The Head Scientist of Borneo Futures, Erik Meijaard, stated that the loss of such a population is very significant for a species with such a small number. "When combined with ongoing pressures such as habitat degradation and human-wildlife conflict, this situation further emphasizes the urgency of implementing a coordinated conservation action plan supported by adequate resources," Erik said in a written statement on Wednesday, June 10, 2026.

The study also found that about 8,300 hectares of forest or 11.7 percent of forest cover in the West Block of Batang Toru were affected by the landslide triggered by extreme rainfall. Professor of Climate Science at Imperial College London, Friederike Otto, mentioned the close connection between climate change and the loss of biodiversity.

"By increasing the intensity of rain in Cyclone Senyar by up to 50 percent, human-induced climate change turns severe tropical storms into triggers of destructive landslides," Otto said.

To determine the influence of climate change on the event, the researchers used climate attribution methods. The analysis results indicate that human-induced climate change increased rainfall intensity during Cyclone Senyar by 9 to 50 percent.

After the flash flood that destroyed settlements in Tanjung Karang Village, Aceh Tamiang Regency, Aceh, on December 12, 2025. Tropical Cyclone Senyar, which formed in the Malacca Strait at the end of November 2025, triggered extreme weather anomalies in the Sumatra region. This phenomenon led to severe flash floods and landslides. Until early December 2025, the National Disaster Mitigation Agency (BNPB) recorded hundreds of casualties and nearly a million residents forced to evacuate in all affected areas. Tempo/Ilham Balindra

Professor of the Department of Biology at the University of Indonesia, Jatna Supriatna, described the loss of dozens of Tapanuli orangutans due to a landslide as a major blow to the world's rarest great ape species.

"To prevent the first extinction of a great ape species in the modern era, Indonesia must provide permanent protection for the Batang Toru Ecosystem," he said. He added that conservation efforts require international support through faster and adequate biodiversity recovery funding.

Similarly, primatologist Serge Wich from Liverpool John Moores University said extreme weather events can have a significant impact on small and fragmented animal populations. "Losing so many apes in this way is very tragic. This is very concerning for the future of this species," Moores said.

Meanwhile, landslide researcher Dave Petley from Nottingham Trent University stated that the landslide material flow is directly linked to the river flow system. The landslide occurs rapidly and is highly damaging. "Those in the path of the landslide barely have any warning or opportunity to save themselves," he said.

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