It only takes a storm cloud and a lot of heat on the surface to trigger a hot blow like the one in Cullera. It is not something common and the most normal thing is that the cloud downloads in the form of a storm. However, according to Daniel Santos, a meteorologist at the Danish Meteorological Center and a researcher at the Complutense University of Madrid, “they can occur in any storm and what it will depend on is the conditions below.”
What is a DANA, how does climate change affect it and how to mitigate flash floods
For Santos, the important thing, rather than thinking about “prohibiting or otherwise regulating” music festivals or similar celebrations in summer, is “taking into account the weather forecast to take protective measures” in all kinds of events. The meteorologist rules out that the high temperatures that have been recorded this summer will be the only factor that determines whether a torrential autumn awaits us: “One of the conditions for DANAS to occur is that there is that heat and that the temperature of the sea it is warm, but then there are multiple other factors that influence”.
What exactly is a warm blowout?
Let us imagine that we have a storm and that, during the storm, instead of heavy rain falling, during the descent of the rain there are meteorological conditions in which the rain evaporates, which causes the air temperature to rise and generates a fall strong winds to the surface.
To give us an idea, it is a phenomenon that always occurs under a storm cloud, a cumulonimbus, it is as if we squeezed a balloon and the cloud pushed the air down.
It is a literal collapse of the air inside a storm cloud.
Do they occur every summer?
Yes of course. It always occurs in storm clouds, what happens is that there are different forms. Inside a storm cloud, you can have normal thunderstorm precipitation or extreme precipitation, if the storm gets very heavy.
If the meteorological conditions include very warm air and the precipitation evaporates on the way down, what is generated is a dry storm. Just a wind storm. If, in addition, the conditions are much more favorable, with winds of 50, 60 or 80 kilometers per hour, it is more favorable for this to occur. If the cloud collapses completely, what occurs are blowouts.
Those blowouts can be both hot and humid. It could be a collapse of the entire cloud and if there are conditions on the surface that are not extremely dry and warm, what would fall is a very strong downpour. In this case, what happened is that since the entire environment was very dry in the lower layer of the atmosphere, when the precipitation fell, it dried up and what was generated was wind.
It’s like turning a bucket of water upside down. The storm does not fall little by little, but we take the lid off and everything falls at once
Is this type of storm more dangerous because it is unexpected?
Depends. The problem with storms is that many times we know that due to a storm it can rain in your town and not rain in the next town. In addition, it is that it changes in a few moments. The extension of the cloud that generates them, if it is a single storm, is a very small extension compared to other phenomena such as a front or in more generalized rains.
The first problem is its location. Storms are very punctual and can fall anywhere, whether it is wet or dry, it generates different problems. One is by wind, and the other is by wind and precipitation, and precipitation can be extreme as well and at a very local point.
It’s like turning a bucket of water upside down. The storm does not fall little by little, but we remove the lid and everything falls at once. It is as dangerous from the wind as it can be from the precipitation, because there are also wet blowouts.
Are they only produced in the east of the Peninsula?
No. They can occur in any storm and what it will depend on is the conditions below, whether it is humid or warm. The most normal thing is that they are normal storms, without being blowouts. But if the weather is right, there can be hot, humid blowouts anywhere.
How long can a hot blowout last?
It’s a matter of minutes. It is a very extreme phenomenon. The cloud compresses the air on the way down and when it reaches the ground, the air quickly comes out from the sides generating a very strong wind. There is another phenomenon that was detected in Cullera and that is that the temperature rose brutally, that is why it is a hot blowout. When the water evaporates in the fall, a phenomenon called adiabatic heating by subsidence occurs, that is, the air heats up a lot when it goes down and suddenly you go from 30º to 40º. There is very hot air and a lot of wind, that is what ends up happening.
All this occurs in a very specific site the size of the cloud, with such bad luck that, in this case, in Cullera, it affected a site where there were many people. But he was warned that there were conditions for blowouts and strong storms.
Are more produced when temperatures are higher?
No, there is not a correlation. What is clear is that when you are hot, the air rises and for storm clouds to be generated, the powerful heating of the ground helps a greater generation of storm clouds.
The fact that there are storm clouds also requires that there be a supply of humidity and that it be very hot on cloudless days, such as today when the sky is blue, no matter how hot it is, it does not generate storm clouds.
Many times we hear about evolution clouds. When the sun warms the ground, the air begins to rise. On their ascent, if there is enough moisture, clouds begin to form. That’s where storm clouds start to form. In other words, warming is part of it, but if we don’t have moisture in the atmosphere we won’t have clouds. Due to the fact that a summer is very hot, if there is no humidity, basically what you can have is a clear sky all day and a lot of heat.
We had a see-saw, which was the climate, which was very balanced, but suddenly someone came who took it out of balance. That someone has been human activity
Are they related to climate change?
Can’t tell right now. What we do know is that the number of extreme events, both storms and more aggressive phenomena, everything seems to indicate that, due to the instability generated by a change in temperatures, they can be favoured. But it is not clear that a particular event can be assigned to climate change.
We know that all climate simulations and all future scenarios seem to indicate the number of severe events of all kinds is on the rise. Simply because the system has become unstable. We had a see-saw, which was the climate, which was very balanced, but suddenly someone came who took it out of balance. That someone has been human activity. So the lurches it hits are bigger. And those lurches are the extreme phenomena.
What has been favored due to the sudden warming due to human activity is that everything is not as smooth as it was before. Then extreme events appear that also appeared before, but we see that the frequency of some rises.
After what has happened in Cullera and knowing that it is something that can happen every summer, shouldn’t the infrastructures and the size of the summer festivals be reconsidered?
The issue is that at the time you have a warning for extreme phenomena, I am not sure if AEMET issued a warning for storms or a warning for winds [La Generalitat Valenciana activó el viernes una alerta por el fuerte calor y viento de poniente]what should have been done is to take protective measures.
Perhaps if the structures on which the festival was set up were not capable of withstanding those gusts of wind, what they would have to think about, if the risk was high, was to cancel or evacuate. It is not so much a question of prohibiting, but, as it is a special situation, of taking measures.
Just like when you cancel other events or other activities when you have very strong winds or snow forecasts. It is not about prohibiting or otherwise regulating, but rather taking into account the weather forecast to take protective measures.
Can a strong gust of wind be distinguished from a convective blowout with the naked eye?
It’s hard. There are some things that are noticeable. The way to know in theory, in a dry blow, would be to realize first that there is a storm and then that there is an excessively high temperature despite the storm. They are small indications, but knowing it at the last moment is quite complicated. When it happens, you have the feeling of what is happening, but you need to confirm the profile of the atmosphere to know if it is that phenomenon.
The feeling is that there is a storm, that it is very hot and that the air is very dry. But it cannot be conclusive.
What should we do if we see that a blowout of these characteristics is approaching us?
The same as when there are gusts of wind. Stay away from structures, move away from trees, seek shelter inside a building or inside a house, and avoid ledges or possible falling flower pots. The same recommendations that are usually made when there are strong winds, such as a DANA.
Now that you name the DANAS. Is it true that the high temperatures recorded this summer predict a torrential fall?
No. You don’t have to. There is no such direct cause and consequence. It is a multifactorial thing. One of the conditions for the DANAS to occur is that there is that heat and that the sea temperature is warm, but then there are multiple other factors that influence the DANAS to be more or less torrential.