how it is formed, how it differs from a normal storm and how to act in one of them

It rains in the Levant. Deluge. Injuries, dozens of homes flooded, infrastructure unusable, rivers overflowing. Deaths. As you may have seen, there are no links in the three sentences that head this paragraph. And it is not an oversight: there are no links because, sadly, they are not necessary.

Every year, for too many now, the end of summer ends with torrential rains in the east of the peninsula and the Balearic Islands. How is it possible that the same improvisation scenes are always repeated? Why are we not prepared for what, by all accounts, seems inevitable? What is a DANA and what should we know about them?

Difference between DANA and cold drop

Around 1886, a group of German meteorologists they started talking of kaltlufttropfen (‘cold air fall’). It may seem that ‘cold drop’ is a native and traditional way of calling certain types of meteorological events, but no. Our ‘cold drop’ comes directly from there: from a way to describe “cold air pockets” or stormy phenomena at altitude”.

A description that is more than a century old.

For this reason, there was a moment when the AEMET decided to start talking about Isolated Depressions at High Levels. The DANA concept is more current and, therefore, more accurate: it describes a cold depression at high levels, isolated from the main circulation, which generates instability by interacting with warm and humid air in lower layers.

But, be careful, the change was not only due to a scientific issue. As the Agency itself recognized‘cold drop’ began to become synonymous with “catastrophic, intense and damaging rains, as well as highly dangerous meteorological situations.” And this is not always the case: we know for a fact that there are DANAs that cause absolutely nothing.

It is something very similar to what he has done in recent days giving a proper name to dangerous DANAs. So for practical purposes, DANA is a more precise way than Gota Fría to talk about one of the most characteristic (and potentially dangerous) atmospheric phenomena of the Spanish autumn.

How a DANA is formed

The mechanism behind Isolated Depressions at High Levels is quite well known. At high levels of the atmosphere, the jet stream is disturbed, undulated, pinched. And finally, it comes off.

That’s what we call an ‘isolated closed low’; that is, detached from the main flow. This low remains circulating independently and, when it interacts with areas of warmer and more humid air (for example, in the Mediterranean) it can generate vertical instability, intense convective attacks, deep clouds and torrential rains.

Why DANAs are increasingly common in Spain

The truth is that there is no consensus that DANAs are increasing in Spain. It is something that is being discussed; But there are indications that some factors are making the episodes more extreme.

We talk about things like the Mediterranean being warmer than usual (a warmer sea contributes more water vapor to the air), the atmosphere also it’s hotter (and has more latent energy) and that the polar jet is becoming more erratic. All this means that even if the same DANAs occur as in previous years, the effects are much worse.

Consequences of DANAs

That’s where the problems begin. Although the effects may vary depending on intensity, duration and location, the fact that DANAs become more intense is what is making our lives difficult.

And it is thatThe catalog of consequences is very extensive..

Flash floods, river flooding, dry riverbed overflows; damage to infrastructure (roads, bridges, urban drainage) and agricultural crops; very numerous human risks: trapped people, power outages, evacuations; and a high economic impact: reconstruction, insurance, losses in tourism or agriculture.

DANAs and climate change

As I said, there is no clear consensus about the appearance of more DANAs than normal. The IPCC reports, for example, do not state any of this; but yes the favorable conditions for extreme phenomena they increase.

In fact, in the Mediterranean regions, warming scenarios foresee an increase in precipitation very intense in isolated events. In other words: as I have been arguing, the climate change It does not create more DANAs, but it makes them more dangerous and difficult to predict.

DANAs in other parts of the world

In the rest of the world, what we call ‘DANA’ is often called ‘cut-off lows’ and, indeed, they are very common in many parts of the world. This type of phenomenon is also observed in the USA, Australia and South America.

However, it is something especially relevant in our country because our climate, the extremely warm sea and such abrupt relief They make isolated casualties our daily bread.

Precautions before the arrival of a DANA

That makes more relevant than ever the fact that be prepared. In that sense, there are a handful of:

• Consult official alerts: AEMET, public administrations and Civil Protection.
• Avoid driving on secondary roads, dry riverbeds and flood-prone tunnels.
• Do not cross watercourses.
• Seal or check drains, roofs and sewers to avoid backups.
• In houses, lift belongings from the floor if water is expected to enter. Take refuge in high areas.
• Have prepared a basic ‘survival’ kit: flashlight, radio, chargers, water, important documents.

In short, the best defense against a DANA is accurate information, preparation and prudence.

Image | The Tampa Bay Estuary Program

In Xataka | What is cold drop, why it seems more intense than ever and why it is not correct to call it that