The current change in the weather in Central Europe was already noticeable in northern Italy a few days ago. Heavy thunderstorms with locally more than 150 litres of rain per square metre initiated the change. When these low pressure areas move from the western Mediterranean through Italy, Austria and Hungary to Poland, this is referred to as a Vb weather situation (pronounced: 5b).
According to Geosphere Austria, Vb locations are responsible for 45 percent of extreme precipitation events in Austria and the Czech Republic. In the past, this has often led to flooding situations. Temperature differences in particular favor such weather conditions, which could become more extreme in the future.
Low pressure areas meet over the Alps
A Vb low is a low pressure system that forms over the Gulf of Genoa and then moves towards northern Italy and the Balkans. In the Alps, the warm, humid air from the south meets polar cold air that flows in from the north. “You can imagine it as if a stone in a stream were to form eddies as the water flowed past,” Cristian Resch, meteorologist at Geosphere Austria, described the situation in an interview with SALZBURG24 on Tuesday. In this case, the stone in the stream is the Alps.
VB lows more intense due to climate change
In Austria, on the other hand, this can cause a lot of precipitation and lead to major damage. The devastating floods in Salzburg in 2002 and 2013, for example, were caused by such weather conditions. The frequent occurrence of Vb low-pressure areas in clusters is also conducive to possible flood situations and is therefore problematic. In a study presented in 2019, hydrologist Günter Blöschl from the Institute of Hydraulic Engineering and Engineering Hydrology at the Technical University (TU) Vienna and climate researcher Michael Hofstätter (then ZAMG) came to the conclusion that the phenomenon of such Vb lows is not increasing, but that they would like to occur more frequently.
According to Geosphere, the number of such weather conditions is actually decreasing slightly due to the climate crisis. “However, the events are becoming more intense because the warmer the air is, the more moisture it can absorb, which then comes back down as rain,” explained Olefs.
Nine to ten Vb lows per year
During the observation period of the study from 1959 to 2015, so-called Vb cyclones occurred more frequently between September and April than in the warmer months from May to October. In their study, Blöschl and Hofstätter identified a total of exactly 557 Vb lows between 1959 and 2015, or nine to ten per year.
The name of such Vb lows goes back to the German meteorologist Wilhelm Jacob van Bebber and has no specific meaning. In 1891, Bebber categorized the paths of low pressure systems and assigned them certain codes. According to Geosphere, the Roman numeral V (5) identifies the center of origin of the low over the western Mediterranean and distinguishes, for example, cyclones that move north over France and Spain (Va) from those that move eastward towards the Balkans (Vc).
(Source: SALZBURG24/APA)
