Spain and other parts of Europe are going through this week by an extensive heat wave that has been accompanied by forest fires, some of great magnitude.
The State Meteorology Agency of Spain (AEMET) had issued for this Tuesday a red notice of extreme danger for the province of Seville, as well as for parts of the province of Córdoba, both in the south of the country, because it was foreseen that they could record temperatures up to 44 ° C.
They also warned the high temperatures will remain until the beginning of next week and that in many parts of the country could be located between 40 ° C and 42 ° C.
The heat wave in Spain has been particularly aggravated by the occurrence of numerous forest fires in different provinces. In some of these, such as the one in the town of Tres Cantos, on the outskirts of Madrid, fire teams have faced great difficulties to extinguish the fire due to winds and dry climate.
According to José Luis Camacho, spokesman for the AEMET, a meteorological phenomenon has been contributing in Spain to the generation of these fires: dry storms.
Such phenomena “make the fire originate in a short time, spread quickly by the wind and, if the place is inaccessible, that the means of extinction take to arrive,” Camacho told the Europa Press agency.
The official warned that this week the conditions of time are combining so that dry storms occur in some parts of Spain, although some wets are also expected to offer relief.
But what are such dry storms and why do they contribute to fires?
Rays fall, but it doesn’t rain
Maybe once on a summer afternoon you have heard the resonar of thunder, but you don’t see rain falling. That could be a dry storm.
In this phenomenon, atmospheric conditions are generated to produce rainfall, as in any storm, but because the air under the clouds is very hot or dry, the rain evaporates before reaching the ground.
However, if there are electric storm conditions, the rays can reach the surface. And when the vegetation on the ground is dry, and the scarce or no rain does not moisten it, the fall of rays can start fires, explains the meteorologist of the BBC Helen Willetts.
In regions where time conditions have generated a very dry environment, as has happened this summer in Spain, a light rain cannot counteract fire spread.
“If the weather has been warm and dry for a prolonged period, a greater amount of rain is required to moisten the fuel bed and reduce the possibilities of lightning ignition,” explains the US National Oceanic and Atmospheric Administration Office of the US.
Lightnings that fall when there are less than 2.5 mm of rain are considered dry. (A millimeter of rain equals one liter per square meter).
In a study published in 2022, scientists identified the following necessary conditions to produce dry lightning:
- High temperatures on the surface at the ground level.
- Dryness in the low troposphere.
- Humidity and instability in the middle troposphere
Dmitri Kalashnikov, researcher at Washington State University in the northwest of the United States and main author of that study, said that due to multiple ignitions, dry rays fires are difficult to control.
“It contrasts with a fire caused by humans,” said Kalashnikov. “That type of fire, is caused or accidental, is limited to a town and usually occurs in places near those that are easier to access.”
On the other hand, dry storms can produce fires anywhere, including remote or difficult access areas for fire combat equipment.
These conditions are those that have been registered in Spain and that have caused the spread of forest fires.
Rays and thunder
Common storms, which imply water precipitation to the ground, occur when air is very unstable or volatile.
They are the result of a rapid rise of the air, something similar to the steam that rises from a cup of hot tea, explains Willetts. But once the air cools, condenses and forms dark and dense clouds called cumulonimbus.
Ascending air continues to feed these storms while they begin to rumble. It is the form of the nature of rebuilding energy in the atmosphere.
Within the storms, the warm and humid air moves quickly up and down, and the ascending currents push the air above the freezing level, so that the water drops of the air become ice or hail.
Thus, within the storm clouds there is a mixture of ice and water, which rub each other and transfer electric charges. This causes an electric charge accumulation and, when it reaches sufficient magnitude, it is released in the form of lightning.
When lightning occurs, Willetts explains, this is able to heat the air until reaching about 30,000 ° C.
The air heats so quickly that it expands suddenly creating a shock wave, a huge vibration in the air.
That is what we hear like thunder.
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