No warning: Deadly flood follows typhoon-burst barrier lake in Taiwan

A barrier lake formed by landslides triggered by July’s typhoon burst its banks in eastern Taiwan on Tuesday as Super Typhoon Ragasa swept across the island, unleashing a flood that killed at least 14 people, injured 32 and left 46 unaccounted for.

The Matai’an Creek barrier lake sits about 11 kilometers (7 miles) upstream of communities in Guangfu Township, Hualien County, and held roughly 91 million tonnes of water — enough to fill about 36,000 Olympic-sized swimming pools. About three-quarters of that water was released when the lake breached its banks, washing away a bridge, uprooting trees and submerging vehicles as it rushed down from the mountains. Emergency services said the floodwater reached metres in some parts of Guangfu and rose to as high as the second floor of homes in areas along the town center.

Survivors in Guangfu said they received no warning from authorities immediately before disaster struck, while academics noted that the event had been anticipated in some monitoring networks. The deputy commander of Taiwan’s Central Emergency Operation Centre said the academic community had warned that the barrier lake could overflow this time, but stressed that evacuations were not always carried out uniformly and that timely warning remains a challenge. Officials had anticipated the flood would take about two hours to reach populated areas downstream; in reality, water from the barrier lake moved quickly, pouring into Guangfu within an hour and forcing residents to scramble for higher ground.

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On Monday, the day before Ragasa neared the island, Hualien authorities issued warnings and evacuated about 7,000 people, setting up three evacuation centers. The central government had urged the county to accelerate evacuations, but county officials said the plan was not mandatory and urged residents to move to higher ground rather than issuing a compulsory order. A high school administrator in Guangfu, who helped run an evacuation center, recounted hearing the lake had overflowed only shortly before water flooded the campus, submerging the sports field and flooding classrooms as staff and evacuees dashed to safety. The administrator added that many of those affected were elderly residents who struggled to evacuate, highlighting gaps in reach for door-to-door alerts and other communications.

Awa, a 42-year-old bookshop owner who moved her inventory to the second floor for safety, said the flood felt like a river surging through the street with cars floating by. She and her husband had only recently relocated their shop and were able to reach higher ground in time, but the water left their store soaked with mud and many of their Indigenous-history books ruined. Awa’s experience underscores the broader impact on Guangfu, a town of about 12,000 people where the elderly are a significant share of the population and many residents do not use smartphones.

The disaster comes as Taiwan operates more than 80 barrier lakes across the island, many formed since the 1970s by landslides and sediment deposits from typhoons and earthquakes. National researchers have noted that barrier lakes formed from looser earth and rock can present a far greater risk when breached, because there are fewer pathways for rapid drainage and fewer access routes for heavy machinery. Taiwan’s public-television service notes that barrier lakes have formed 88 times since the 1970s, with 57 percent created by typhoons and 23 percent by earthquakes; most disappear within a year, though four have persisted for decades.

Experts say public understanding of barrier lakes remains limited, and even where warnings exist, rural and aging communities can be slower to evacuate. Taiwan’s geography — much of Hualien County sits in rugged, mountainous terrain near the Pacific Ring of Fire — makes rapid emergency response difficult, and residents have long faced hazards from typhoons and earthquakes. The county’s tourism-dependent economy, including access to Taroko Gorge National Park, has already been battered by disasters in recent years, including a 2024 magnitude-7.1 earthquake.

In Guangfu, residents continue to contend with the consequences of the flood as search-and-rescue teams and volunteers assess debris and look for missing relatives. Local authorities said the toll could rise as more bodies are recovered from homes where water surged to upper floors, and the situation remains precarious for those displaced by the floods. The death toll, the number of missing and the full impact on Guangfu’s residents illustrate how a single hydrological event can ripple through a rural town, even when the storm itself does not pass directly overhead.

Additional reporting by Lok Lee of BBC News Chinese in Taipei.