What kind of events happen every year

Extreme events Extreme weather events cause damage running into the millions every year. What role does climate change play in this? How can we avoid damage?

Natural disasters in Germany - an overview

Extreme natural events are inherent in the dynamic planet earth and are therefore part of our environment. They can also cause enormous damage in Germany. Whether natural events turn into catastrophes depends on the susceptibility and preparedness of society.

The number and intensity of such extreme events are subject to strong fluctuations. Due to the greenhouse-related increase in the sensitive and latent energy components in the atmosphere, an increase in weather-related extreme events is to be expected in the future. However, above all, increasing concentration of values ​​and susceptibility lead to the expectation of greater damage from natural hazards.

What natural hazards are threatening Germany?

The atmosphere and the lithosphere (= solid rock shell of the earth) are the main sources of extreme natural events. Storms, heavy precipitation, hail events, heat and cold waves and lightning strikes can be ascribed to the direct atmospheric effects. This results in storm surges on the coasts, flash floods in steep catchment areas or in built-up areas and flooding by river floods.

© KlausMJan / Fotolia - Low water on the Rhine

Drought periods due to persistently high temperatures with high evaporation rates and forest fires are also indirect atmospheric effects. The processes of the solid rock shell up to 100 km deep can cause earthquakes and volcanic eruptions. Although there are currently no active volcanoes in Germany, volcanologists speak of the possibility that eruptions can occur again in the Eifel. Landslides, mudslides and avalanches can be caused by the atmosphere or the lithosphere or by the interaction of various triggers. A landslide can be triggered by lighter earthquakes in combination with atmospheric preconditions such as prolonged precipitation and heavy snow cover.

Natural hazards caused by extraterrestrials are seldom considered, but nevertheless possible. Solar eruptions lead to magnetic storms which, for example, can result in large-scale power outages as a result of interference currents in overhead lines or malfunctions of satellites with disruptions to navigation or communication systems. The most devastating natural disasters imaginable are meteorite impacts with impact craters up to several 100 kilometers in diameter and global effects. In addition, humans are to be mentioned as the trigger or intensifier of disasters, e.g. in the case of deliberately set forest fires or in the case of avalanches and landslides on deforested areas. The last man-made event was the landslide on a former spoil dump of an open-cast lignite mine in Nachterstedt, Saxony-Anhalt, in July 2009. Earth masses slid 40 m deep into a residual open pit lake and tore several buildings with it. This disaster claimed three lives and 41 people lost their homes.

© Michl / Fotolia - Storm damage by Kyrill

The overall economic damage natural hazards can cause is shown by the last major natural disasters in Germany, the winter storm Kyrill 2007 with damage amounting to 4.2 billion euros (Munich Re 2008) and the Elbe flood in 2002 with damage amounting to 11.8 billion euros . Euros (Munich Re 2007). If one looks at all natural events in the period from 1970 to 1998, it becomes clear that storm events are the most expensive natural hazards in Germany. They account for 75% of the total economic damage. 19% are caused by river floods and flash floods, 5% by other atmospheric hazards such as heat waves, frost and forest fires. Earthquakes and landslides contributed a small share of 1% to the overall economic damage in these three decades (Munich Re 1999).

However, it cannot be concluded from these figures that earthquakes and storm surges are negligible. Rough calculations estimate that worst-case events (e.g. storm surge in the Hamburg area, strong earthquake near Cologne or Frankfurt) can lead to economic damage in the order of tens of billions of euros. For example, paleoseismological studies have shown an earthquake with a moment magnitude of 6.7 in the Lower Rhine Bay near Cologne. A comparison of flood and earthquake risk for the urban area of ​​Cologne showed that for extreme events with a low probability of occurrence (less than approx. 200-year events) the effects of an earthquake outweigh those of a flood (Grünthal et al. 2006).

Spatial and temporal scope of natural hazards

Figure 1 shows possible natural hazards for Germany with their spatial and temporal impact areas. Events with a small, locally limited area of ​​influence of up to 10 km are mainly convective heavy precipitation events and flash floods, thunderstorms, lightning strikes and hail.

© K. Günther

Avalanches and earth mass transports such as landslides, mudslides and landslides also have a very local effect. Other natural hazards can affect much larger areas. Tornadoes, for example, have train lengths of up to 100 km, whereas the effective train width is usually not greater than 500 m. Floods caused by storm surges, as in 1962 in Hamburg and Bremen, or river floods, as in 2002 on the Elbe and Danube, are effective regionally or supra-regionally along coastal sections or river valleys, up to several 100 km. Earthquakes, volcanic eruptions and magnetic storms also fall into this category. Throughout Germany, i.e. with areas of influence greater than 500 km, natural hazards act like winter storms with wind fields up to 1000 km wide and train lengths up to 5000 km. Cold and heat waves are also effective on the entire area of ​​Germany. Drought and drought can result in damage to agriculture in entire regions, impaired inland navigation and bottlenecks in electricity production due to insufficient cooling capacity of the warmed-up rivers.

The duration of extreme natural events varies. The timescale ranges from a few seconds to months. In most cases, a longer duration of action leads to greater damage. Short event durations of seconds and minutes have lightning strikes, tornadoes, mass movements and avalanches, as well as earthquakes and meteorite strikes. With an extremely short duration of action, the latter release such a large amount of energy that they could devastate areas the size of Germany. Evidence of this is the Nördlinger Ries on the Swabian Alb, an impact crater with a diameter of 24 km that was formed around 14.5 million years ago (Munich Re 1999). Hail, heavy precipitation, flash floods, winter storms, forest fires, floods, volcanic eruptions and magnetic storms have a longer effect; they usually last for hours to a few days. Cold and heat waves in particular last a few days to a few months. Long-term high temperatures in particular are a great burden on the human cardiovascular system and repeatedly lead to numerous heat deaths. This happened in the record summer of 2003, when the mean temperature from June to August was 3.4 ° C above the climatological mean value for the period 1961-1990. There were 9,000 fatalities in Germany and over 70,000 in the whole of Europe. The total economic damage was put at 1.3 billion euros (Munich Re 2008 and 2009).

Damage from extreme natural events has increased dramatically in the last few decades, both globally and in Germany. Various influences contribute to this increase, such as increasing settlement of endangered areas, accumulation of values, changed susceptibility due to increasing interconnectedness of our society, or climate change. Due to the diversity of these influences and the random nature of the causative natural processes, it is still hardly possible to quantify the individual proportions of the various influences.

The article is used with the kind permission of the Ernst & Sohn publishing house as an excerpt from:
Climate research: Droughts in Germany could become more extreme

Researchers at the Alfred Wegener Institute (AWI) analyze data from the last millennium and come to the conclusion that future droughts in Germany could be more extreme.