Storms become more catastrophic since 1990

Storms have been more catastrophic in the Europe since 1990, according at a research report.

The researchers of the Finnish Meteorological Institute (FMI) showed that storm-induced forest damage went through a change point in 1990 and after 1990 the worst storms have been 3.5 times as catastrophic as before, mainly because of climate change, said a press release.

The FMI has investigated intense, large-scale storms based on their impacts on primary forest damage in Europe over the period 1951 to 2010. It was already known that storm-induced primary damage has grown in that period, but it was considered to be mainly due to the increase in total growing stock and forest management practices, such as preference for Norway spruce.

However, the FMI researchers found that storm-induced forest damage went through a statistically significant change point in 1990.

“After 1990 the worst storms have been 3.5 times as catastrophic as before. This type of change cannot be caused by a change in forest management practices. Instead it is related to a change in storm climate,” said FMI Head of Unit Hilppa Gregow.

The study also addressed the storms’ gust wind speeds that have been measured since the 1980’s. Gregow said in all of the most catastrophic storms, which include Wiebke (1990), Lothar (1999), Martin (1999), Gudrun (2005), Kyrill (2007), and Klaus (2009), the highest gust speeds were between 50 and 60 m/s.

It has been recently shown that the stems of all kinds of trees will break when wind speed exceeds 42 m/s, whereas Norway spruce can be uprooted also at lower wind speeds.

“Therefore, the change point in forest damage in 1990 may at least partially be due to the strongest storms having more widespread gusts with wind speeds exceeding 42 m/s,” said Gregow.

The FMI study also found that the worsening of the catastrophic storms is a wintertime (December-February) phenomenon, whereas the intensity of the strongest autumn storms has decreased since 1990. Gregow said although the North Atlantic Oscillation (NAO) correlates with storminess in general, the studies were not able to relate the 1990 change point to changes in NAO. Climate change, on the other hand, could have an impact on the storms. For example, recent studies have found simultaneous changes in the Arctic Ocean summertime ice cover, and North Atlantic wind climate.