Cyclone Senyar landslide kills 7 percent of Tapanuli orangutans

A devastating landslide, triggered by extreme rainfall from Cyclone Senyar in November 2025, has resulted in the deaths of approximately seven percent of the critically endangered Tapanuli orangutan population. This finding is the central focus of a new study published in the journal Current Biology.

The landslide occurred in the western block of the Batang Toru ecosystem, the primary habitat for the remaining Tapanuli orangutans. Researchers from Borneo Futures and World Weather Attribution analyzed satellite imagery and orangutan density estimates to determine the impact. Their analysis suggests that around 58 Tapanuli orangutans perished in the landslide, representing about 11 percent of the population in the West Block and seven percent of the total wild population.

Erik Meijaard, Head Scientist at Borneo Futures, emphasized the severity of this loss for a species with such a small population. He stated that this event, combined with existing pressures like habitat degradation and human-wildlife conflict, underscores the urgent need for a coordinated and well-resourced conservation plan.

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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.

The study also revealed that the landslide affected approximately 8,300 hectares of forest, or 11.7 percent of the forest cover in the West Block of Batang Toru. Professor Friederike Otto from Imperial College London linked the event directly to climate change, noting that human-induced warming increased the rainfall intensity of Cyclone Senyar by nine to 50 percent, turning a severe tropical storm into a trigger for destructive landslides.

Tropical Cyclone Senyar caused widespread extreme weather anomalies across the Sumatra region in late November 2025, leading to severe flash floods and landslides. Earlier in December 2025, flash floods had already destroyed settlements in Tanjung Karang Village, forcing nearly a million residents to evacuate and resulting in hundreds of casualties, according to the National Disaster Mitigation Agency.

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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.