BMKG: Sumatra Disasters Triggered by Extreme Rain in Late November 2025

In late November 2025, flood and landslide disasters struck dozens of regencies/cities spread across three provinces on Sumatra Island, namely Aceh, North Sumatra, and West Sumatra.

According to the Meteorology, Climatology, and Geophysics Agency (BMKG), these disasters were triggered by extreme rainfall.

Based on BMKG criteria, rainfall above 150 millimeters (mm)/day is classified as high. However, rainfall in several areas of Sumatra in late November 2025 exceeded that threshold.

"The rainfall from November 25, November 26, to November 27 was so extreme it reached 'black' levels," said BMKG Head Teuku Faisal Fathani during a meeting with House of Representatives Commission V on Monday (1/12/2025).

"The highest recorded was even 411 mm per day in Bireuen Regency [Aceh], which is even higher than the monthly rainfall there; this amount poured down in a single day, and imagine this happening for three days," he continued.

"This is what caused such massive hydrometeorological disasters, as the soil or land could not withstand such a large deluge of rainwater, leading to flash floods, landslides, and floods," Teuku stated.

Not only in Bireuen, but during the period of November 25-27, 2025, BMKG also recorded extreme rainfall with an intensity of more than 150 mm/day in several surrounding areas, such as:

• North Aceh (Aceh): 310.8 mm/day
• Medan (North Sumatra): 262.2 mm/day
• Central Tapanuli (North Sumatra): 229.7 mm/day
• Padang Pariaman (West Sumatra): 154 mm/day

"Tropical Cyclone Senyar, which formed in the Malacca Strait, significantly influenced the increase in rainfall intensity in the surrounding areas, including Aceh, North Sumatra, and West Sumatra," BMKG said in a press release (27/11/2025).

Sumatra's Disasters Not Solely Triggered by Rain

Nevertheless, some other parties believe that the cause of Sumatra's disasters was not merely rain, but also vulnerable environmental conditions.

This was, for instance, stated by Dyah Murtiningsih, Director General of Watershed Management and Forest Rehabilitation (PDASRH) at the Ministry of Forestry.

According to Dyah, in addition to high rainfall intensity, Sumatra's disasters were influenced by changes in land cover.

"These changes in land cover are not only within forest areas but also outside forest areas, whose function should be to absorb water," Dyah said, as reported by Katadata.co.id (28/11/2025).

A similar sentiment was expressed by Hatma Suryatmojo, a hydrology researcher from Gadjah Mada University (UGM). He believes Sumatra's disasters were influenced by environmental damage, particularly in watershed areas.

"The flash flood tragedy that struck Sumatra in November 2025 is essentially an accumulation of 'ecological sins' in the upstream watershed," Hatma said in a press release (1/12/2025).

"The extreme weather at that time was merely a trigger; the destructive power that occurred is inseparable from the severe environmental damage in the upstream to downstream areas of the watershed," he added.

Meanwhile, the Indonesian Forum for the Environment (Walhi) believes that the main cause of the disaster is ecological vulnerability due to the conversion of forests into extractive industrial land, one example being oil palm plantations.

"We know that oil palm's function is not to regulate water systems, but rather to damage the water cycle," said Walhi Campaigner, Uli Arta, to Katadata.co.id (28/11/2025).

"When forests are converted into oil palm monocultures, floods and landslides become an inevitability that will continuously recur," she stated.