Four days of extreme rain in Indonesia killed 7% of world’s rarest great apes, study finds
Extreme Rain in Indonesia Threatens 7% of World's Rarest Orangutans, Study Finds
Four days of extreme rain in Indonesia triggered a catastrophic event that claimed the lives of 7% of the world’s most endangered great apes—the Tapanuli orangutan—according to a recent study. The unprecedented rainfall, which fell in North Sumatra during November 2025, caused massive landslides that obliterated nearly 8,300 hectares of critical habitat. This disaster, linked to climate change, highlights the growing vulnerability of the species, with 11.7% of their remaining habitat lost in a single incident. The findings serve as a stark reminder of how extreme weather can accelerate the decline of already threatened wildlife.
Climate Change Intensifies Rainfall, Amplifying Ecological Impact
Researchers from Liverpool John Moores University, Borneo Futures, and World Weather Attribution analyzed the effects of Cyclone Senyar on the Tapanuli orangutan population. The study combined satellite data with field assessments to reveal that human activities increased the rainfall’s intensity by up to 50%, making the event more severe. The West Block of the Batang Toru ecosystem, already strained by mining and palm oil expansion, bore the brunt of the disaster, resulting in the deaths of 58 individuals from a population of around 800. This loss underscores the intersection of climate-driven extremes and habitat degradation.
The research team emphasized that such extreme weather events are becoming more frequent due to climate change, posing a direct threat to the orangutans’ survival. “This type of weather event can have significant population-level consequences,” noted Prof Serge Wich, a co-author. “In fragmented habitats, even small changes can lead to irreversible declines.” The study’s data shows that the rainfall exceeded historical averages, creating conditions ripe for landslides that devastated the species’ home.
Habitat Loss and Conservation Challenges
The Batang Toru ecosystem, a key refuge for the Tapanuli orangutan, has long been under threat from deforestation and infrastructure projects. The recent landslide compounded these pressures, reducing genetic diversity and isolating the population further. “The event was a demographic shock,” said Prof Jatna Supriatna of Universitas Indonesia. “If we don’t act now, this could be the first modern extinction of a great ape species.” Conservationists stress that protecting the remaining habitat is critical to preventing such losses in the future.
Experts recommend a temporary moratorium on land-use activities in the Batang Toru region to allow for recovery. The Indonesian government has already paused major projects to assess the damage, but long-term solutions require sustained funding and international collaboration. The study’s results align with global concerns about how climate change interacts with human activity to push species toward extinction. Without urgent intervention, the Tapanuli orangutan’s survival may hang in the balance.
Global Response and Biodiversity Recovery Efforts
International conservation groups are calling for immediate action to safeguard the Tapanuli orangutan. The study’s authors argue that biodiversity recovery financing must be prioritized to mitigate the impact of future extreme weather events. “This isn’t just a local crisis—it’s a global one,” said one researcher in a blockquote. “The loss of 7% of the world’s rarest apes is a clear signal that climate change is reshaping ecosystems at an alarming rate.”
Efforts to restore the damaged habitat include replanting native vegetation and reinforcing riverbanks to prevent future landslides. While the Indonesian government has taken initial steps, scientists warn that without global support, the orangutans’ plight may worsen. The event serves as a wake-up call for policymakers, emphasizing the need to integrate climate resilience into conservation strategies. As the planet faces more frequent extreme weather, protecting vulnerable species like the Tapanuli orangutan becomes increasingly urgent.