STORY: Deforestation and natural resource extraction fueled severe flooding on Indonesia's island of Sumatra after last week's rare tropical storm.

That is according to local environmental groups.

Official numbers show more than 700 people have died in landslides and flash floods.

Tommy Adam is the head of environmental advocacy at the Indonesian Forum for the Environment, or WALHI.

"This disaster was not a natural disaster. This is an ecological disaster caused by the mismanagement of natural resources by the government. WALHI West Sumatra has calculated that in West Sumatra alone, the deforested area from 2001 until 2024 has reached 800,000 acres of wet forest."

:: WALHI Sumbar

Indonesia, the largest economy in Southeast Asia, has long faced criticism for deforestation.

It is home to thick tropical rainforests, many of which have been heavily logged. 

Now the country aims to reverse some of the damage, but still relies on natural resources to grow its economy.

From 2001 to 2024, North Sumatra province lost around 4 million acres of tree cover.

That's 28% of the tree cover area in 2000, according to international monitoring group Global Forest Watch.

David Gaveau is an environmental researcher.

"It really started in the late 60s. The forest started to be exploited for its timber, its natural timber. And once all the good valuable timber was exploited, was extracted, then the forest didn't really have economic value anymore in people's eyes. So it got converted to oil palm primarily, but also to acacia and eucalyptus plantations for pulp and paper."

"So now we've got an island that has 25 percent of its landmass still covered in forest. That represents 11.7 million hectares of forest left. That's 25 percent of the total landmass of Sumatra. This is the island of Indonesia that has had the most deforestation indeed, yes."

Many people in the flood zone share the concerns. 

This resident describes illegal loggers as "people with mischievous hands", and blames them for the massive amount of timber swept away by the floods.

Now Indonesia's environment ministry says it will question eight companies operating in the flood-affected areas in relation to logging, mining and palm plantations. 

That's according to local media reports, which did not name specific companies or projects.

Indonesia's forestry and environment ministries did not reply to a Reuters request for comment.