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Peer-reviewedCC BYCurrent Biology

Extreme rainfall further endangers the world’s rarest great ape

  • Erik Meijaard1
  • Muiz Wafiy2
  • Safwanah Ni’matullah3
  • Rona Dennis3
  • Panut Hadisiswoyo4
  • Douglas Sheil5
  • Adrià Descals6
  • David Gaveau7
  • Nabillah Unus3
  • Hjalmar Kühl8
  • Friederike E. L. Otto9
  • Jatna Supriatna10
3 more authors
  • Edvin Aldrian11
  • David Petley12
  • Serge A. Wich13
13 affiliations
  1. 1School of Biological and Environmental Science, Liverpool John Moores University, Liverpool L697ZB, UK; Durrell Institute of Ecology and Conservation, University of Kent, Canterbury CT27NR, UK; Borneo Futures, Bandar Seri Begawan BS8811, Brunei Darussalam. Electronic address: [email protected]
  2. 2School of Biological and Environmental Science, Liverpool John Moores University, Liverpool L697ZB, UK
  3. 3Borneo Futures, Bandar Seri Begawan BS8811, Brunei Darussalam
  4. 4Orangutan Information Centre, Selayang, Kota Medan, Sumatera Utara 20131, Medan, Indonesia
  5. 5Forest Ecology and Forest Management, Wageningen University & Research, Wageningen 6708 PB, the Netherlands
  6. 6Department of Biology, University of Antwerp, 2000 Antwerp, Belgium
  7. 7TreeMap, Montpellier 34000, France; Jeffrey Sachs Center on Sustainable Development, Sunway University, 5, Jalan Universiti, Bandar Sunway, Petaling Jaya, Selangor 47500, Malaysia
  8. 8Senckenberg Museum für Naturkunde, 02826 Görlitz, Germany; International Institute Zittau, Dresden University of Technology, 02763 Zittau, Germany
  9. 9Centre for Environmental Policy, Imperial College London, South Kensington, London SW71NE, UK
  10. 10Department of Biology, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok 16224, Indonesia
  11. 11Meteorology and Climatology, BRIN, Jakarta 16911, Indonesia
  12. 12Nottingham Trent University, Nottingham NG14FQ, UK
  13. 13School of Biological and Environmental Science, Liverpool John Moores University, Liverpool L697ZB, UK. Electronic address: [email protected]
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Abstract

In late November 2025, over 1,000 mm of precipitation fell within four days across North Sumatra, triggering widespread landslides and flooding in the West Block of the Batang Toru ecosystem, the core habitat of the critically endangered Tapanuli orangutan (Pongo tapanuliensis), estimated to contain 581 individuals (95%CI [180–1,201]) prior to the event [1]. Using pre- and post-event Sentinel-2 and PlanetScope satellite imagery, we quantified the extent of forest loss. Initial analysis indicates that 3,964 hectares of previously intact forest were swept away by landslides and floods. An additional 2,487 ha of scars is extrapolated from areas that are cloud-covered in the Sentinel-2 image. These scar estimates were combined with a 1km² density surface from a 2016 survey to estimate the number of orangutans potentially affected. Our results indicate that 33-54 individuals may have been impacted, with a substantial proportion likely killed by landslides, treefall, or flooding. Given that annual mortality exceeding 1% is sufficient to drive this species to extinction, our preliminary estimate of 6.2-10.5% mortality suggests a critical demographic shock. We call upon the Indonesian government and the international community to take immediate action and provide support to ensure the survival of the Tapanuli orangutan. The government is urged to enact emergency protections, halt habitat-damaging development, and expand protected areas to restore critical lowland forest, with essential financial and technical support from the global community.

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Cite

BibTeXRIS
BibTeX
@article{meijaard2026extreme,
  title = {{Extreme rainfall further endangers the world’s rarest great ape}},
  author = {Erik Meijaard and Muiz Wafiy and Safwanah Ni’matullah and Rona Dennis and Panut Hadisiswoyo and Douglas Sheil and Adrià Descals and David Gaveau and Nabillah Unus and Hjalmar Kühl and Friederike E. L. Otto and Jatna Supriatna and Edvin Aldrian and David Petley and Serge A. Wich},
  journal = {Current Biology},
  year = {2026},
  month = jun,
  doi = {10.1016/j.cub.2026.05.029},
  url = {https://doi.org/10.1016/j.cub.2026.05.029},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - Extreme rainfall further endangers the world’s rarest great ape
AU  - Erik Meijaard
AU  - Muiz Wafiy
AU  - Safwanah Ni’matullah
AU  - Rona Dennis
AU  - Panut Hadisiswoyo
AU  - Douglas Sheil
AU  - Adrià Descals
AU  - David Gaveau
AU  - Nabillah Unus
AU  - Hjalmar Kühl
AU  - Friederike E. L. Otto
AU  - Jatna Supriatna
AU  - Edvin Aldrian
AU  - David Petley
AU  - Serge A. Wich
PY  - 2026
DA  - 2026/06/01
JO  - Current Biology
DO  - 10.1016/j.cub.2026.05.029
UR  - https://doi.org/10.1016/j.cub.2026.05.029
AB  - In late November 2025, over 1,000 mm of precipitation fell within four days across North Sumatra, triggering widespread landslides and flooding in the West Block of the Batang Toru ecosystem, the core habitat of the critically endangered Tapanuli orangutan (Pongo tapanuliensis), estimated to contain 581 individuals (95%CI [180–1,201]) prior to the event [1]. Using pre- and post-event Sentinel-2 and PlanetScope satellite imagery, we quantified the extent of forest loss. Initial analysis indicates that 3,964 hectares of previously intact forest were swept away by landslides and floods. An additional 2,487 ha of scars is extrapolated from areas that are cloud-covered in the Sentinel-2 image. These scar estimates were combined with a 1km² density surface from a 2016 survey to estimate the number of orangutans potentially affected. Our results indicate that 33-54 individuals may have been impacted, with a substantial proportion likely killed by landslides, treefall, or flooding. Given that annual mortality exceeding 1% is sufficient to drive this species to extinction, our preliminary estimate of 6.2-10.5% mortality suggests a critical demographic shock. We call upon the Indonesian government and the international community to take immediate action and provide support to ensure the survival of the Tapanuli orangutan. The government is urged to enact emergency protections, halt habitat-damaging development, and expand protected areas to restore critical lowland forest, with essential financial and technical support from the global community.
SN  - 0960-9822
SN  - 1879-0445
ER  -