A catastrophic weather event in Indonesia has devastated the critically endangered Tapanuli orangutan population, with a new study documenting the deaths of 58 individuals following four days of intense rainfall in November 2025.
The extreme precipitation, which exceeded 1,000 millimeters (39 inches) in North Sumatra province, represents a major blow to the species' survival prospects. The 58 deaths account for 11% of the local population in the West Block of the Batang Toru ecosystem and 7% of the entire global population, which numbers fewer than 800 individuals in the wild.
Researchers used satellite imagery analysis combined with population density estimates to assess the impact of Cyclone Senyar on the orangutans. The storm caused widespread environmental destruction, with approximately 8,300 hectares (20,510 acres) of critical forest habitat devastated by landslides triggered by the extreme rainfall. This represents 11.7% of the key forest area where these apes live.
Climate change has intensified the rainfall threat. Scientists determined that human-induced climate change caused by fossil fuel burning increased the rainfall intensity by up to 50%, transforming what might have been a severe weather event into a catastrophic one for the vulnerable primate population.
The findings carry urgent implications for the species' future. Previous research indicates that annual population losses of just 1% would eventually lead to extinction. With the Tapanuli orangutan already facing habitat destruction from mining operations, palm oil plantations, and a hydropower project, the impact of climate-driven disasters compounds existing conservation challenges.
"It is tragic to lose so many apes in this way," said Professor Serge Wich, a primatologist at Liverpool John Moores University and study co-author. "In landscapes where populations are small and fragmented, this type of weather or climate event can have population-level consequences. It is extremely worrying for the future of this ape."
Professor Jatna Supriatna of Universitas Indonesia emphasized the global stakes: "To prevent the first modern extinction of a great ape species, Indonesia must permanently protect the Batang Toru ecosystem, but our international partners must also meet their global commitments by providing immediate biodiversity-recovery financing."
The Indonesian government has temporarily paused major industrial activities in the Batang Toru area to allow scientists to investigate how to secure the species' long-term survival while also assessing risks to human populations. Researchers from Borneo Futures, World Weather Attribution, and Liverpool John Moores University recommended an immediate moratorium on land-use activities that degrade orangutan habitat, alongside expansion of protected areas to stabilize the remaining population.
The Tapanuli orangutan was only scientifically described in 2017, making it the world's newest and most endangered great ape species.