Jakarta. The deadly flash floods that struck multiple regions across Sumatra have been made significantly more destructive by years of large-scale deforestation, which triggered landslides and washed heavy debris into residential areas — a pattern not seen in recent floods in Thailand, Vietnam, and the Philippines, according to an environmental expert.

Logs and large debris swept from degraded forest areas caused extensive infrastructure damage and contributed to higher fatalities as they crashed into residential zones. In many locations, landslides triggered by heavy rains compounded the destruction.

Bayu Dwi Apri Nugroho, an environmental climatology expert at Gadjah Mada University, said the key difference between the floods in Indonesia and those in neighboring countries lies in watershed conditions and the extent of environmental degradation. Sumatra, he noted, has suffered from years of deforestation due to logging, land clearing, and mining activities.

“Once the forest disappears, the soil’s ability to absorb water drops drastically. Even a short episode of extreme rain can cause severe river overflows,” Bayu said in an interview on Sunday.

This is why flash floods in Sumatra frequently carry large volumes of logs and mud, Bayu added — a phenomenon rarely seen in Thailand, Vietnam, or the Philippines.

“The level of deforestation in those countries is nowhere near as severe as in Indonesia. Our upper-watershed damage is much worse,” he stressed.

Floods and landslides in Aceh, North Sumatra, and West Sumatra have claimed more than 300 lives and displaced tens of thousands of people. In Aceh alone, floods and landslides destroyed 12 bridges and cut off inter-provincial roads at 14 locations, with significant infrastructure damage also reported in North Sumatra and West Sumatra.

Bayu noted that poor spatial planning, weak oversight and unregulated land use have further exacerbated disaster risks. He urged the government to accelerate forest rehabilitation efforts and strengthen law enforcement.

“Flash floods in Sumatra will become more frequent and increasingly destructive,” Bayu warned.