Apriadi Gunawan, Medan – An independent survey found 330 landslides upstream of the Garoga and Siondop rivers after the rare tropical cyclone Senyar struck South Tapanuli regency in North Sumatra in late November
Conducted by the National Coordination Center of Nature-Loving Students Units (Mapala) and environmental activists, the survey found the most landslide spots, at 245, in the Garoga upstream river area, while the Siondop River had 85.
Survey team head Decky Chandrawan said that 330 landslides were identified in surveys across the two areas. The survey was carried out on Jan. 21-27 with direct observations, by studying the river's flow and using drones for wider coverage.
He said the survey would continue in the near future in several other potential landslide areas, especially those located in the operational areas of several companies recently closed by the government, such as PT NSHE and PT AR.
Decky said he wanted to prove how many landslides there were in areas near these companies.
Most landslides upstream of the Garoga and Siondop rivers were in open forest areas.
Surveyors even found a completely deforested area on top of a mountain that had been turned into a palm oil plantation. He said the deforested part had been located above Muara Sibuntuon village, Central Tapanuli regency, which borders the Batangtoru protected forest.
He said clearing forests for palm oil plantations had been done on a huge scale, and mostly carried out by corporations, with only a small portion cleared by local villagers.
"Almost 80 percent of opened forests has been turned into palm oil plantations," Decky told The Jakarta Post on Thursday.
"The forest coverage is already damaged, so the scale of the landslides in the area were quite high."
He said landslides in November had mostly affected people living on steep slopes, riverbanks and deforested areas with vegetation degradation.
This strengthened suggestions that the disasters were not only caused by extreme weather, such as high rainfall, but also accumulated land conversion activities and weak supervision in water catchment areas, he added.
He said this indicated a failure to protect rivers upstream areas, which are the last line of defense to maintain the natural balance.
"Forests, which should function as a protector [from extreme weather], instead are put under increasing pressure," he said.
"If current conditions continue, the potential [increases] for future disasters [...] that threaten public safety and housing."
Decky said that based on the survey results, the organizer put forward several urgent recommendations, including transparent audits on activities and licensing of areas upstream of the Garoga and Siondop rivers, a moratorium on activities potentially damaging forest in water catchment areas and strict law enforcement against violations in forests and riverbanks.
He also pushed for the restoration of forests in the river upstream areas based on the scientific study and people's participation and involvement in the public and independent institutions to monitor conditions of forest areas continuously.
"Without policy changes and real actions, South Tapanuli territory will remain in cycles of natural disasters triggered by environmental damage in the river upstream areas," Decky said.
Commenting on the survey results, Siti Wahyuna from the North Sumatra Natural Resources Conservation Agency's (BBKSDA) Region III Padangsidempuan, said a limited budget and personnel shortages were the main obstacles to monitoring forests.
"We have limited budget and personnel to conduct [forest] patrols," she said during a talk show on the condition of forests in the Tapanuli area, South Tapanuli, on Tuesday.
Cyclone Senyar made landfall in northern and western parts of Sumatra on Nov. 25, 2025, bringing extreme rainfall and strong winds that triggered widespread flooding and landslides across Aceh, North Sumatra and West Sumatra.
At least 3.1 million people were affected, with 1,204 confirmed deaths, some 7,000 injured and around 140 still missing as of Tuesday, according to the National Disaster Mitigation Agency (BNPB).
South Tapanuli regency was among the worst affected by flash floods and landslides in North Sumatra. Based on data from North Sumatra Disaster Mitigation Agency, as of Jan. 11 there were 93 people dead, 48 wounded and four missing people. (nvn)