DWD: For the past there is no clear evaluation showing change in the strength and intensity of storms over Germany
By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
(German text translated/edited by P. Gosselin)
This month two major North Sea storms have hit Europe rather severely, and not surprisingly the usual climate ambulance chasers were out in force to try to pin the blame on man’s activity, and in doing so ignored the climate history that provides us with the proper perspective. We look at some analyses of past German storm activity.
Two years ago Uwe Kirsche of the German DWD national Weather Service warned RP-Online against jumping to conclusions:
Germany appears to be plagued by storms. Over the past tens years there’s been on average one hurricane-force storm each year. Are these natural events occurring more often than they did in the past? Will storms accompany us on a daily basis during certain months?
‘That’s a difficult topic,’ answered Uwe Kirsche of the German DWD Weather Service. ‘For the past there are not such evaluations showing a change in the strength or frequency of storms over Germany,’ he clarified. While temperature curves and rainfall amounts are well documented over decades, the DWD must hold back when it comes to storms.”
At ScienceSkepticalBlog,Michael Krüger reported in 2014:
Storm activity over the North and Baltic Seas (storm index at the North and Baltic Sea / geotropical wind speeds since 1880) has not been increasing, but rather have been falling off since 1880. A temporary peak was reached around 1990 and since then activity has fallen further.”
Here Kruger shows two storm index curves, but without citing a source. Researchers at the Institute for Coastal Research at the Helmholtz Center in Geesthacht have tracked storms in Germany and neighboring countries for a long time, and they too have not been able to detect any worrisome trends. At the online shz.de in 2014 we read:
Storm ‘Christian’ was no offspring of climate change
[…] Together with colleagues of the German Weather Service and the Danish Meteorological Institute, coastal researchers of Geesthacht evaluated the data on storm ‘Christian’ and other intense storms. Von Storch experienced the October 28, 2013, storm up close as while attempting to visit his home island of Föhr, he became stranded in Dagebüll. He and his colleagues found fluctuations in storm intensity over many decades. ‘Detectable is a reduction in storm intensity from the 1880s until the mid 1960s, followed by a rise until the mid 1990s,’ said von Storch. Since the 1990s, activity has fallen off once again. ‘Unlike heat waves, these fluctuations can be attributed solely to natural variability,’ explained the scientist. […]”
Hans von Storch also was interviewed in der Zeit in 2015 (behind a paywall):
‘Sometimes it just gets more active…’
Waiting for the intense storm: Meteorologist Hans von Storch knows what extreme weather events have to do with our everyday climate.”
Noteworthy is also an article appearing in proplanta: in January, 2015:
Climate experts warn against rushing to blame storms and flooding on climate change
‘Single events cannot be linked to climate change,’ told Florian Imbery, climate expert at the German DWD Weather Service in Offenbach, to the German Press Agency on Monday. Reliable statements can be made only when we compare 30-year intervals. We can determine relatively well changes in the temperature. With precipitation it’s already more difficult, and it’s practically impossible to do with storms. The difference: ‘Temperature is a stable magnitude, precipitation and wind are highly variable in terms of space and time.’ For Imbery it is relatively clear that it is getting warmer: ‘We are getting heat periods more often.’ But that is the only significant change in climate – for wind in rain their are only ‘signs’.”
Read at proplanta
Four recent papers find no trend
Now let’s look at long-term observations. Bierstedt et al. (2016) looked at the variability in daily wind speed over northern Europe for the past 1000 years in computer simulations. The results are easily summarized: Every model shows something different. The study ended up with a large contradiction and the finding that the models are still unable to simulate wind and storms. That’s a pity. Abstract:
Variability of daily winter wind speed distribution over Northern Europe during the past millennium in regional and global climate simulations
We analyse the variability of the probability distribution of daily wind speed in wintertime over Northern and Central Europe in a series of global and regional climate simulations covering the last centuries, and in reanalysis products covering approximately the last 60 years. The focus of the study lies on identifying the link of the variations in the wind speed distribution to the regional near-surface temperature, to the meridional temperature gradient and to the North Atlantic Oscillation. Our main result is that the link between the daily wind distribution and the regional climate drivers is strongly model dependent. The global models tend to behave similarly, although they show some discrepancies. The two regional models also tend to behave similarly to each other, but surprisingly the results derived from each regional model strongly deviates from the results derived from its driving global model. In addition, considering multi-centennial timescales, we find in two global simulations a long-term tendency for the probability distribution of daily wind speed to widen through the last centuries. The cause for this widening is likely the effect of the deforestation prescribed in these simulations. We conclude that no clear systematic relationship between the mean temperature, the temperature gradient and/or the North Atlantic Oscillation, with the daily wind speed statistics can be inferred from these simulations. The understanding of past and future changes in the distribution of wind speeds, and thus of wind speed extremes, will require a detailed analysis of the representation of the interaction between large-scale and small-scale dynamics.”
Another study by Bett et al. 2017 examined wind in Europe over the past 142 years, apparently based on homogenized data. The scientists were not able to find any really significant long-term trend, but were able to see systematic fluctuations on decadal scales, likely in connection with ocean cycles. Abstract:
Using the Twentieth Century Reanalysis to assess climate variability for the European wind industry
We characterise the long-term variability of European near-surface wind speeds using 142 years of data from the Twentieth Century Reanalysis (20CR), and consider the potential of such long-baseline climate data sets for wind energy applications. The low resolution of the 20CR would severely restrict its use on its own for wind farm site-screening. We therefore perform a simple statistical calibration to link it to the higher-resolution ERA-Interim data set (ERAI), such that the adjusted 20CR data has the same wind speed distribution at each location as ERAI during their common period. Using this corrected 20CR data set, wind speeds and variability are characterised in terms of the long-term mean, standard deviation and corresponding trends. Many regions of interest show extremely weak trends on century timescales, but contain large multidecadal variability. Since reanalyses such as ERAI are often used to provide the background climatology for wind farm site assessments, but contain only a few decades of data, our results can be used as a way of incorporating decadal-scale wind climate variability into such studies, allowing investment risks for wind farms to be reduced.”
Next is a paper by Rangel-Buitrago et al. 2016 in the Journal of Coastal Research. The authors examined wave and storm data from a buoy off the coast of South Wales. Near the end of the 20th century they observed a high level of storm activity, but this subsided during the early part of the 21st century. Here the researchers were able to see clear relationships with ocean cycles, especially the Arctic Oscillation and the North Atlantic Oscillation. Abstract:
Wave Climate, Storminess, and Northern Hemisphere Teleconnection Patterns Influences: The Outer Bristol Channel, South Wales, U.K.
This paper investigates potential climate-change impacts on the Outer Bristol Channel (Wales, U.K.) by analysing a 15-year wave-buoy dataset (1998–2013) to characterise wave climate and storms. The research showed that the increasing storminess experienced during the latter half of the 20th century did not, as expected, continue into the first decades of the 21st century; however, the wave climate showed clear cyclic variation in average monthly significant wave height (Hs), with low values occurring between May and August (Hs < 1.4 m, Hsmax < 6 m) and a minimum in August (Hs = 1.3 m, Hsmax = 5.2 m). Monthly mean wave power was 27.4 kwm−1, with a maximum of 951 kwm−1 during December. The 267 storm events were recorded during the assessment period. Storm-severity distribution presented a log-normal trend, with weak and moderate events making up 73% of the record (125 and 69 events, respectively); significant (18%), severe (4%), and extreme (6%) storms resulting in 73 events that are more destructive made up the remainder of the record. Fifty-five percent of the monthly averaged wave variations, wave power, and storminess indices are linked to several teleconnection patterns, the most relevant being the Arctic Oscillation, with 23.45%, the North Atlantic Oscillation, with 20.65%, and the East Atlantic with 10.9%. This kind of characterization is essential for design considerations to any proposed developments within the Bristol Channel that affect the coastal zone, e.g., the proposed design of the Swansea Bay Tidal Lagoon, which is capable of generating over 542,000 MWhyr−1 of renewable energy.”
Also see CO2Science.
Finally we go to Krakow, where Bielec-Bakowska & Piotrowicz 2013 analyzed the storm past of the last 100 years. Summary: There is no detectable trend. Abstract:
Long-term occurrence, variability and tracks of deep cyclones over Krakow (Central Europe) during the period 1900–2010
This article discusses patterns in the long-term and seasonal occurrence of deep cyclones over Krakow. This study analysed the frequency of occurrence of air pressure values equal to or lower than the 1st percentile (equivalent to ≤995.3 hPa) of all air pressure values recorded at 12:00 UTC over a period of 110 years (1900/1901–2009/2010). Special attention was devoted to the tracks of deep cyclones. No distinct changes were found in the frequency of occurrence of deep cyclones during the study period. Overall the frequency peaked in December, but in recent years there has been an increase in frequency towards the end of winter and beginning of spring. A similar general lack of noticeable change in the number of days with deep cyclones can also be found in specific tracks. There were minor increases in the frequency of occurrence of cyclones from the Norwegian Sea (T1), the Atlantic (T3), Bay of Biscay (T6) and the Mediterranean (T7) after 1950. The study also found confirmation of the theory that cyclone tracks had shortened at their northeastern extremities.”
Also read the article on the paper at The Hockeyschtick.
October 31, 2017 at 10:26AM