DANA and gota fría: why September to November is flood season

Key rules

• Season: Flood risk is highest from September to November, though a DANA can happen in any month.
• Warning time: Formal warnings usually come 24 to 72 hours ahead, but flash floods in small catchments can develop within an hour or two of the rain.
• Gota fría: Gota fría and DANA mean the same thing in everyday use.
• Red warning: Red means extreme danger, so plan to stay put and avoid travel.
• Most exposed areas: The Mediterranean coast and the Balearic Islands are hit most often.

What a DANA is

A DANA is a pocket of cold air high in the atmosphere that has split off from the main jet stream and sits on its own. When it lies over warmer air near the ground, the atmosphere becomes unstable. That can mean intense storms, heavy rain, hail and flooding. A DANA can stay in the same place for days.

You will also hear "gota fría" in the news and from neighbours. It means the same kind of event, so treat the two words as one. The weather service prefers "DANA" because not every DANA brings cold at ground level, and not every heavy-rain episode comes from one.

When it happens

Flood risk is highest from September to November. The Mediterranean Sea is at its warmest then, and cold air arrives high above it. A DANA can happen in any month. Spring (April and May) is a second, smaller risk period. Late summer and winter episodes are less common.

Where it hits hardest

The Mediterranean arc is the most exposed:

• the Valencian Community, including Valencia and Alicante provinces
• Murcia
• eastern Andalucía (Almería, Granada, Málaga)
• Catalonia
• the Balearic Islands

Albacete and parts of Aragón can also be hit. Inland and Atlantic areas are affected less often. If you live or plan to rent in one of these areas, take autumn seriously.

How much warning you get

Formal weather warnings usually come 24 to 72 hours before a DANA, and they are updated as the event gets closer. A possible DANA is often flagged in forecasts several days ahead.

The general area at risk is predicted fairly well. The exact spot and strength of storm cells are not. Totals can differ greatly over a few kilometres, and a warning can be raised or lowered at short notice. Flash floods in small catchments can develop within an hour or two of the rain. A dry riverbed or ravine can fill fast, even if it is not raining where you are.

What the warning colours mean

Warnings are issued by zone. Red means extreme danger. The red rain levels are set separately for each warning zone, as millimetres of rain in 1 hour and in 12 hours, and they are highest in the wettest Mediterranean zones. Ask your town hall for the figures for your zone, because they are revised from time to time.

The decision, timeline and checklist below show how to react at each warning level and what to do before the season starts.

Choosing between options

How should you react to the warning level for your area?

• Keep watching the forecast: A possible DANA is flagged several days ahead but no formal warning has been issued for your zone yet.

• Prepare and limit travel: A formal warning is issued for your zone, usually 24 to 72 hours before, and rain is expected in your area.

• Stay put and avoid all travel: A red rain warning is issued for your zone, which means extreme danger.

Follow the highest warning level issued for your zone, and keep checking, because warnings can be raised or lowered at short notice.

Check the red-warning figures for your warning zone with the national weather agency, AEMET.

Timeline and deadlines

• Flood risk is highest in the Mediterranean east: September to November

• A possible DANA is flagged in forecasts: several days ahead

• Warnings can be raised or lowered, so keep checking the forecast: at short notice, up to the rain itself

Checklist

• Learn that a DANA is a pocket of cold air high in the atmosphere that has split off from the main jet stream and can sit over warm Mediterranean air for days.

• Treat "gota fría" and DANA as the same thing when you hear them in the news or from neighbours.

• Find which AEMET warning zone your home or workplace is in.

• Treat a red warning as extreme danger and plan to stay put and avoid travel.

What to watch out for

• Autumn is the main flood season: Flood risk from a DANA is highest from September to November, but a DANA can happen in any month, including spring and late summer. Stay alert to forecasts all year if you live on the Mediterranean coast, in the southeast or the Balearic Islands.

• Some regions are hit far more often: The Valencian Community, Murcia, eastern Andalucía, Catalonia and the Balearic Islands are the most exposed. Albacete and parts of Aragón can also be hit. If you live, rent or travel in these areas, check the flood risk before you choose a home and know your local warnings.

• Warning time is short: Formal weather warnings usually come 24 to 72 hours before a DANA, and they can be raised or lowered at short notice. Local rain totals can differ greatly over a few kilometres. Check the forecast daily when a DANA is flagged and do not rely on a single warning.

• Flash floods can come very fast: Flash floods in small catchments can develop within an hour or two of the rain, even before you see heavy rain where you are. Act on the first warning and do not wait to see the water rise.

• Red means extreme danger: A red rain warning is set at different levels for each zone, and the wettest Mediterranean zones have the highest levels. Treat red as an order to stay safe and avoid travel, and ask AEMET or your town hall what red means in your zone.

Floods in Spain: quick answers

Is it safe to cross a dry rambla after rain?

No, do not cross a dry rambla or barranco during or after heavy rain, because water can arrive suddenly from rain falling upstream. The same goes for flooded roads and underpasses, on foot or by car. Wait until the authorities say it is safe and move to higher ground.

When should I move my car away from a rambla or underground garage?

Move your car before the storm warning takes effect, while it is still safe to do so. Park it away from ramblas, riverbeds, ravines and low-lying or underground parking. Once heavy rain has started, leave the car where it is: it can be replaced, a life cannot.

Are sandbags or flood barriers worth buying for my home?

They are only worth it for a low-risk door in a spot that gets shallow water, because against a flash flood they have limited effect. Fast, deep, debris-laden water can leak through, overtop or push them over, and it also enters through drains, walls and floors. Moving people and belongings upward matters more, along with insurance and keeping drains clear.

Does the government certify or subsidise flood barriers for homes?

No, there is no general official programme that certifies or subsidises sandbags or barriers for homes. Some councils and fire services do use them. Ask your council what it offers in your area.