After the storm, there is always heavy rain, causing many places to face the risk of flooding, flash floods and landslides.
During the period from 8:00 p.m. on September 7 to September 8, many northern provinces recorded very heavy rainfall, exceeding 400 mm in some places such as Pu Danh 417 mm (Son La); Van Mai 343 mm (Hoa Binh); Nam Xay 2 – 383 mm (Lao Cai); Ta Si Lang 425 mm (Yen Bai)… Soil moisture models show that some areas have almost reached saturation (over 85%), unable to “hold” more water, while the rain will continue in the coming days.
Flash floods are particularly dangerous, experts say, because they can occur anywhere more rain falls than the ground can absorb. Plus, they happen incredibly quickly.
Topography and geography play a major role in how land responds to heavy rainfall. Water rises very quickly, with large changes possible even in small areas, so predicting exactly where flash floods will occur is a major challenge.
Flash floods often occur when a storm rages over an area for hours, accompanied by heavy rain. This causes rivers, streams, and even storm drains to burst their banks, sending water flooding into streets and residential areas.
Mountainous areas are particularly prone to flash floods, according to the National Weather Service (NOAA). There is not much surface area for rainwater to soak into the ground before it slides downhill, flows into streams, floods into valleys and rises rapidly with little warning.
How does a landslide happen? Video: AFP
Areas that have experienced wildfires, especially around mountains, may be at higher risk of flash flooding during heavy rains.
Catastrophic flash floods can also occur when water overtops a dam, or when a dam fails. When this happens, huge amounts of water can flow out with little warning. Such sudden events can submerge entire towns. A prime example is Hurricane Katrina in 2005, when levees broke across New Orleans, causing historic flooding that forced many people to climb onto their rooftops for safety and killed hundreds.
Experts recommend that in the event of a flash flood, immediately move to higher ground. It is necessary to escape floodwaters as quickly as possible, as the water may be contaminated, electrically charged, or contain dangerous animals such as fire ants.
Another tip: Don’t drive on flooded roads. Just 2 feet of fast-moving water can sweep away most vehicles, including pickup trucks and SUVs, according to the National Weather Service. Floodwaters can also pose other hazards, such as road cracks and collapses. If a driver is trapped in a flooded vehicle, abandon the vehicle immediately and seek higher ground, according to NOAA.