Experts explain causes of early-season flash floods in Vietnam’s Lai Chau

Speaking to Tuoi Tre (Youth) online newspaper, Professor Do Minh Duc of the University of Science under Vietnam National University-Hanoi described the disaster as a “multi-hazard event.”

He explained that extreme rainfall overwhelmed slopes previously weakened by smaller landslides, causing soil, rocks, and timber to rush into streams and fields.

Muong Than lies on the edge of the Hoang Lien Son range, where streams drop steeply from 1,500-2,500 meters.

The Nam Sang stream, with a small basin of six square kilometers, has slopes averaging 11-12 degrees.

Temporary natural dams formed by landslide debris stored water and materials until heavy rain broke them, unleashing destructive torrents.

The area’s geology also worsened risks.

Magmatic rock formations and large fault systems left bedrock fractured and weathered, creating thick layers of unstable soil prone to sliding.

Nguyen Van Huong, head of weather forecasting at the National Center for Hydro-Meteorological Forecasting, identified three main factors, including prolonged downpours saturating slopes, steep terrain with fragile soils, and an extreme rain event between last Thursday night and Friday that dumped 262 millimeters in just over a day.

Duc said early warning signs include sudden seepage of water from slopes, cracking sounds of trees and rocks, or streams turning muddy.

Such disasters often strike at night, making vigilance crucial.

Experts recommended checking nearby streams every 15-30 minutes during heavy rain and evacuating immediately if water rises quickly, or even if it unexpectedly drops.

According to the Lai Chau administration, natural disasters caused around VND550 billion (US$21 million) in damage from the beginning of the year to mid-July.

The July 17 flash flood in Muong Than killed six, left two missing, and injured eight.

About 200 households were affected, with 24 losing homes entirely.

More than 1,000 police, soldiers, local officials, youth volunteers, and residents joined rescue and evacuation efforts, moving 1,686 residents in high-risk areas to safety.