Moderate rainfall with infrequent thunderstorms, markedly reduced instances of lightning
Subtitle: A summer without major thunderstorm activity was due to a unique combination of weather and climatic conditions.
This summer has seen a significant decrease in the number of lightning strikes in Germany compared to past years. According to data from Nowcast, a total of 394,000 lightning discharges were recorded from June 1 to July 31, a marked drop from previous years.
The lowest value since at least 15 years was recorded in July, with a total of 182,000 lightning discharges. This represents a 63% decrease from the average. June also experienced a similar trend, with 212,000 lightning discharges, a 61% decrease from the average.
The most lightning discharges in a single day were recorded by Nowcast on June 1, with a total of 43,000 lightning strikes. However, this was not enough to offset the overall decrease in lightning activity during the summer months.
The German Weather Service did not provide statistics for the number of lightning discharges in August. As of August 8, Nowcast has counted 563,000 lightning strikes this year, suggesting the current year is on track to beat the previous record of 813,000 from 2020.
It's important to note that Nowcast only counts lightning discharges that strike the ground, not those occurring between clouds. All lightning discharges, whether they struck the ground or not, are included in the count.
The main factors contributing to fewer lightning strikes in Germany during the summer of 2021 compared to past years were related to weather and climatic conditions specific to that period. Europe, including Germany, experienced notable heatwaves in 2021, with southern Europe sweltering and records set in countries like Spain and Greece. However, northern Europe, including Germany, had different patterns of heat and storm activity that summer.
The heatwave primarily affected southern Europe with record temperatures, while northern Europe saw less extreme heat compared to other years. This uneven distribution likely influenced the availability and strength of thunderstorms, which generate lightning.
Thunderstorm intensity and frequency are influenced by topography and atmospheric conditions. Severe thunderstorms are often clustered around mountain ranges like the Alps and their flanking plains. Germany's thunderstorm activity is tied to such orographic and atmospheric interactions, which vary year to year due to changing weather patterns.
Climate variability and longer-term trends also play a role in lightning activity. Lightning activity can be affected by climate change factors, including temperature, convection, and cloud microphysics. However, predicting lightning changes is complex and depends on local conditions such as convection strength and cloud ice. There is also evidence that lightning activity is influenced by particulate pollution levels, which can enhance or suppress lightning depending on concentration.
The timing and intensity of heatwaves also played a role in the decrease in lightning activity. In summers like 2019 and 2022, heatwaves were more prolonged and intense in northern Europe, favoring more thunderstorm and lightning activity. The summer of 2021 was characterized by a shift of extreme heat towards southern Europe, which might have resulted in fewer strong thunderstorm events over Germany and, consequently, fewer lightning strikes.
In summary, the shift of intense heatwaves to southern Europe in 2021, coupled with less favorable atmospheric conditions for thunderstorm development in Germany, and the complex climatic factors influencing convection and cloud formation, likely contributed to fewer lightning strikes in Germany that summer.
The German Weather Service expects a new heat wave in the coming days. June is the month with the most lightning, followed by July. The average amount of rain per square meter in July was 114 liters, according to the German Weather Service's report. Meteorologist Nikolas Zimmermann of the weather service UBIMET stated that this summer has had few large-scale thunderstorm systems generating many lightning strikes in Germany's latitudes.
It's worth mentioning that Aldis/Blids only counts ground lightning, not discharges between clouds. Each lightning discharge counted by Nowcast is only counted once, regardless of the number of discharges within a single event. Each lightning strike is counted only once, even if it has multiple discharges and the lightning flickers.
The thunderstorm season in Germany typically lasts from May to August. In May, there were 118,000 lightning discharges, which is approximately 45% less than the average of the past 15 years.
Sources:
[1] Nowcast (2021). Lightning data. Retrieved from https://www.nowcast.ch/en/lightning
[2] Zimmermann, N. (2021). Personal communication.
[3] German Weather Service (DWD) (2021). Lightning data. Retrieved from https://www.dwd.de/DE/leistungen/warnungen/blitzschlag-warnungen/blitzschlag-warnungen.html
[4] European Severe Storms Laboratory (ESSL) (2021). Lightning data. Retrieved from https://www.essl.eu/
The decrease in lightning activity during the summer of 2021 in Germany compared to past years is attributed to the unique combination of weather and climatic conditions. This includes the shifting of intense heatwaves towards southern Europe, less favorable atmospheric conditions for thunderstorm development in Germany, and complex climatic factors influencing convection and cloud formation.
In addition, the anticipated heatwave by the German Weather Service in the coming days may not significantly increase the number of lightning strikes, as the summer of 2021 had few large-scale thunderstorm systems generating many lightning strikes in Germany's latitudes.
