Storm surge on the coast: know your zone, leave in time

Several things come together in a storm surge. First, onshore wind – wind blowing from the sea towards the land – pushes the water towards the coast over long distances. Second, the low air pressure in the storm system raises the water level a little further, because less air is pressing down on the sea. Third, the tides play a part: if the storm coincides with normal high tide, the water rises especially high.

Waves come on top. They carry extra water onto land and can strike dykes, walls and houses with great force. The shape of the coast matters too: in bays, river mouths and shallow coastal waters, water can pile up particularly high.

According to the US National Hurricane Center, storm surge has historically been the greatest threat to life in hurricanes. European coasts such as the North Sea and Baltic have their own storm-surge warning services and a system of dykes. The basic rules still apply everywhere.

Many coastal towns have maps showing which areas can flood in a storm surge and which zones are evacuated first. Ask the municipality, civil protection or your accommodation whether your address is in such an area and where the route inland runs. This entry gives no specific water levels or zones – local plans take precedence.

On holiday it is best to ask on arrival day: how are guests warned, and where do you go? If the host country has a warning app, it is worth installing. That way you do not have to find your bearings first in an emergency.

The extent is hard to judge locally. The sea may barely rise in one place and run far inland a few kilometres further on. That is why you rely on the authorities' assessment, not on your view from the window.

Storm surges often have one advantage over other disasters: they are usually announced hours to days in advance. Use that time. When a watch is issued, get your go bag, important documents, medication, charging cables and a power bank ready, fill up the car and talk to neighbours who might need help leaving.

If an evacuation is ordered for your zone, leave immediately and follow the designated route. Do not wait until the last moment: roads can already be flooded before the peak of the surge. Those who stay often cannot be reached by rescuers during the storm.

A typical mistake is refusing to evacuate because the wind seems 'only moderate'. In a storm surge, the water is the main danger, and it can run high even when the weather seems less dramatic.

Do not go to dykes, piers or beaches to watch the waves. Waves and currents can sweep people away, and a single big wave can reach much further up than the others.

If leaving is no longer possible, stay in a safe, tall building only on official instruction and move to the upper floors. Do not retreat into a closed attic without an exit – if the water keeps rising, you are trapped there. If you are in danger, call the local emergency number (112 in the EU).

Floodwater can be contaminated with sewage and chemicals and can hide dangers such as debris, open manholes and power lines. So do not walk or drive through it. Return only when the authorities clear the area; then document the damage before you clean up. Important: tsunamis have their own rules. After a strong earthquake on the coast or if the sea suddenly draws back, go to high ground immediately, even without an official warning.