Floods: before, during, after

A flood happens when more water arrives than rivers, streams and drains can carry away. This can happen after days of rain, when a large river slowly overflows its banks, or after a single violent thunderstorm. The second case is called a flash flood: the rain falls so fast that the ground cannot absorb it, and the water rushes downhill over roads, slopes and small streams. Flash floods can develop within minutes – even where there is no river nearby.

The force of water is almost always underestimated. Moving water does not only push against you, it also washes away the ground under your feet. A car is lighter in water than you would think, because it contains air and therefore gets buoyancy. Once the wheels lose their grip, it drifts with the current. That is why a large share of flood deaths happen in vehicles.

Under murky water you also cannot tell whether the road is still there. The current can undermine asphalt and lift manhole covers. If you walk through, you may step into nothing. That is exactly why there is no safe rule of thumb for “still shallow enough” – the right decision is always: not through.

The most important part happens before the flood. Ask your municipality whether your home is in a flood or heavy-rain hazard area. Many regions have hazard maps showing which areas flood first. Do not store documents, medication and supplies in the basement, and keep a go bag ready.

When a warning comes, time is the most valuable thing. Now is the moment to move people and animals upstairs, charge devices and check the way to a higher place. Do not wait until you see the water rising – with flash floods it is often too late by then. When the authorities call for evacuation, leave immediately.

During the flood: go up, not through. Move to upper floors or higher ground, keep away from banks, bridges and streams, and avoid basements, underground car parks and underpasses. If you are trapped, go to the highest floor – but not into a closed attic without an exit – call the emergency number and make yourself noticeable.

Basements and underground car parks are traps when water is rising. They can fill very quickly, and a door often cannot be opened against the pressure of the water. Nothing in the basement is worth going down for. The same applies to underpasses, where water collects.

Water and electricity are a dangerous mix. Do not touch electrical devices or switches if you are wet or standing in water. Switch off the power only if it is safe to do so; otherwise inform the utility or the fire service. Flood water is also often contaminated with sewage, fuel or chemicals – avoid skin contact, wash your hands thoroughly and throw away food that has touched the water.

An underestimated danger comes during the clean-up: pumps, dryers and generators with combustion engines produce carbon monoxide. This gas has no smell and can be deadly in enclosed spaces. So only run such devices outdoors. And only go back into the house when the authorities allow it – watch for gas smells, damage to the building, power lines and notices about drinking water.

The US National Weather Service coined a motto for the most important rule: “Turn Around, Don't Drown”. It reminds you that turning back is not weakness but the wisest decision. Many people get into danger because they know a road well and believe they know how deep the water is there.

A common mistake in thinking is: “It has always been fine so far.” But heavy rain can also hit places that have not flooded for a long time. Even far from rivers, hollows, slopes and basement flats can be affected. If you know your region's warning channels – radio, warning apps, sirens, announcements – you gain the minutes that matter.

After the flood, it helps to photograph damage before you throw anything away; this makes things easier with your insurance. Wear gloves, sturdy shoes and protective clothing during the clean-up. And accept help: clearing up after a flood is hard work that you do not have to manage alone.