After a storm, heavy rainfall often follows, putting many areas at risk of flooding, flash floods, and landslides.
From 8 PM on September 7 to September 8, several provinces in Northern Vietnam recorded extremely high rainfall, exceeding 400 mm in some locations such as Pú Dảnh 417 mm (Sơn La); Vạn Mai 343 mm (Hòa Bình); Nậm Xây 2 – 383 mm (Lào Cai); Tà Si Láng 425 mm (Yên Bái)… Soil moisture models indicate that some areas are nearing saturation (over 85%), unable to “hold” any more water, while rain is expected to continue in the coming days.
High water levels in Bản Mù, Trạm Tấu district, Yên Bái. (Photo: Yên Bái).
According to experts, flash floods are particularly dangerous because they can occur anywhere that receives rainfall exceeding the land’s absorption capacity. Additionally, this phenomenon happens extremely quickly.
Topography and geography play a crucial role in how land withstands heavy rainfall. Water can rise rapidly, with significant changes occurring even in small areas, making accurate predictions of where flash floods will occur a significant challenge.
Flash floods typically occur when a storm affects an area for many hours accompanied by heavy rainfall. This can cause rivers and streams, even drainage systems, to overflow, pushing water onto streets and residential areas.
Mountainous regions are highly susceptible to flash floods, according to the National Oceanic and Atmospheric Administration (NOAA). There is not much surface area for rainwater to soak into the ground before it quickly slides down slopes, flows into rivers, spills into valleys, and rises rapidly with little warning.
How do landslides occur? (Video: AFP).
Areas that have previously experienced wildfires, especially around mountains, may face a higher risk of flash floods during heavy rains.
Devastating flash floods can also occur when water spills over a dam or levee that is damaged. In such cases, a massive amount of water can surge out with little warning. Such sudden incidents can submerge an entire town. A prime example is Hurricane Katrina in 2005, when levees broke across New Orleans, USA, causing a historic flooding disaster that forced many to climb onto rooftops for safety and resulting in hundreds of fatalities.
Experts recommend that when facing flash floods, immediately move to higher ground. It is essential to get away from floodwaters as quickly as possible, as the water may be contaminated, electrified, or contain dangerous animals like fire ants.
Another important note is to not drive on flooded roads. Just 0.6 meters of fast-moving water can sweep away most vehicles, including trucks and SUVs, according to the National Weather Service (NWS). Floodwaters can also pose many other dangers, such as cracked and collapsed roads. According to NOAA, if flooding occurs while a driver is trapped in a vehicle, they should abandon the vehicle immediately and seek higher ground.
