Weather conditions change over the years, so after decades, so does the climate. An investigation carried out by the Spanish and French has focused on the study of the precipitations in the form of hail registered in the south of France in the last decades.
The study has been published in the journal Atmospheric Research and has studied hail records from 1948 to 2015. What results have you obtained and how important are they?
Hail precipitation
The study observes an evolution towards an atmospheric environment that favors the increase of this meteorological phenomenon, but the researchers believe that other factors could mitigate it and cause that they are actually only increasing in frequency the biggest hail storms, while weak hailstorms diminish.
Because the meteorological conditions that form hail are quite unstable and irregular in space and time, it is quite complex to have a complete database in order to study its evolution and trends.
This study has been carried out by the Group of Atmospheric Physics of the Institute of the Environment of the University of León, jTogether with the Complutense University of Madrid and Anelfa, a research center in Toulouse.
For the reason mentioned above, the study has focused on French regions where there is continuous and uninterrupted data for more than 25 years. Anelfa has more than 1.000 stations that measure hailstorms. . From there, statistical techniques widely used in climatological studies were used to calculate trends.
Records and data
In the Pyrenees region the frequency of hail fall has increased in the last 25 years, depending on the areas analyzed. These dates cannot be extrapolated to other nearby regions since the hail formation conditions are very irregular. If they were precipitations in the form of rain, if it is possible to know the rainfall regime of the regions close to those analyzed.
In an attempt to reach some more solid and generalizable conclusions, given that Spain does not have such continuous data or records of hail, what has been sought is to find relationships between atmospheric fields and hail falls.
In this way, the study has analyzed the trends that atmospheric fields have when they are more prone and favorable to the appearance of hail. The results mark a significant trend in the last 60 years towards more favorable environments for hail storms to form.
However, this trend should not be interpreted as an increase in the frequency of hail registered on the ground, since there are many more factors to take into account, such as the melting of the hail as it falls from the cloud. Many precipitation events in the form of hail do not end up reaching the ground because they return to a liquid state before falling to the ground.
Due to global warming, the most favorable environments and situations for hail storms to occur are occurring with increasing frequency. Although it should also be noted that, with global warming, the level of snow and freezing is getting higher and higher. This height is known as isozero, that is, the height at which a temperature of zero degrees Celsius is found and from which the hail begins to melt.
This produces a greater number of storms with potential hail, but in many of them the hail eventually melts before reaching the ground and only the most severe storms with the largest hail eventually reach the surface.
Hail and global warming
The uncertainty of the frequency of hail is difficult to transfer to global warming scenarios, since it is difficult to predict with models the reliable trends of this phenomenon.
In a warmer atmosphere there is more energy for deep convention to occur, which favors the appearance of storms with potential hail, but at the same time, the increase in the level of the isozero favors its occurrence. the melting of the hail making it less likely to reach the ground. It is difficult to know which of these two events influences the hail the most.