Meteorological Background
During the past few decades, most of Central Europe's major floods have been caused by a so-called Vb (pronounced "five-b") weather situation, and the 2005 flooding in Central Europe was no exception. During a Vb weather event, a low pressure system moves eastward from Iceland and encounters arctic air masses that divert the cyclone to the south toward the Mediterranean, where it picks up warm, moist air. The cyclone then curves toward the northeast and the air is lifted by the mountain ranges of Central Europe. Typically, the result is very intense and persistent rainfall over an extended area.
Figure 2. Typical pathways of cyclones over Europe and a characteristic Vb cyclone track. (Source: AIR) Flood Impact
The 2005 floods were the most expensive natural disaster in Switzerland's history and also caused considerable economic losses in Austria, Germany, Romania, and Bulgaria (see Table 1).
Table 1. Economic and insured losses for the 2005 flood in the worst affected countries
Country |
Core Period |
Economic Losses (Millions of Euros) |
Insured Losses (Millions of Euros) |
Switzerland |
August 14–23, 2005 |
1,870–1,950 |
804–1,580 |
Austria |
August 19–23, 2005 |
515–583 |
150 |
Germany |
August 20–23, 2005 |
185 |
>30 |
Romania |
August 3–9, 2005 |
1,636.9 (includes spring events) |
>12 |
Bulgaria |
August 4–7, 2005 |
436 (includes spring events) |
>12 |
An overview of the impact in each country, as well as post-flood response, is provided in the sections below. After the flood, the affected countries undertook the task of improving flood protection through better communication to the public, information access for scientists, and more resilient physical infrastructure.
However, flood risk is still rising throughout Europe because of increasing concentrations of exposure along flood-prone rivers. Moreover, the tremendous increase in impervious surfaces due to urbanization continues, further increasing the risk—especially from brief, but extreme precipitation that lead to pluvial (or off-floodplain) floods.
Switzerland
Economic losses from the 2005 floods totaled about EUR 2 billion in Switzerland. The cantons of Bern, Luzern, Url, and Obwalden were most affected, representing about 70% of the countrywide losses. Throughout Switzerland heavy rainfall (more than 200 mm within 48 hours in some areas) led to saturated soils. Numerous valleys on the northern slopes of the Swiss Alps, as well as pre-Alpine areas in eastern Switzerland, were affected by flooded mountain streams and rivers.
Figure 3. Flooding in the Ennetburgen, Switzerland, in August 2005. (Source: Swiss Air Force) In several catchments rivers reached 1-in-100-year flows, and at some river gauges new historical records were set. The flooding damaged public infrastructure, as well as residential, commercial, and industrial buildings, and agricultural areas. Several valleys were cut off by ensuing landslides. The last event with a comparable damage pattern occurred in 1910.
Figure 4. High water levels on the Rhein River in Rheinfelden, Switzerland, taken on August 23, 2005. (Source: Timo Newton-Syms, CC BY-SA 2.0) After the 2005 floods, flow regulations were systematically surveyed across all cantons to improve coordination and to provide the maximum possible flood protection for all larger settlements along rivers. Renaturation projects were initiated to give rivers more space and reduce flow velocity. Only two years later, during the 2007 floods, these measures proved successful in many parts of the country. Detailed hazard maps were created after 2005, and improved access to warnings, weather forecasts, and other real-time information was made available.
Austria
In Austria economic losses amounted to more than EUR 500 million. The worst affected states were Tyrol, Vorarlberg, Styria, and Salzburg. Styria received the entire average August rainfall amount between August 20 and August 22, and Tyrol and Vorarlberg received between 120 mm and 240 mm of rainfall in less than 24 hours on August 22, also equaling the monthly average for August. Extreme river flows (up to 1-in-100 years) in Tyrol and Vorarlberg, exacerbated by already saturated soils, resulted in large-scale flooding, exceeding previous events from 1999 (popularly known as "the Pentecost flood") and 2002. The situation was similar in Styria, where landslides followed the heavy rainfall in the southwest of the region. In the city of Graz, several urban streams burst their banks.
Figure 5. Flooding on the Trisanna River in Tyrol, Austria, in August 2005. (Source: Imst District Surveyor's Office) In the past decade, Austria has invested significant resources in improving its flood resilience. Real-time rainfall, river flow data, and flood maps for various recurrence intervals can now be retrieved online. In addition, early flood warning systems were developed for several rivers, and warning systems for major rivers such as the Danube and the Salzach were improved. Many of the measures that were implemented helped to avoid damage during recent floods in the summers of 2013 and 2014, which affected large areas that had also been impacted by the 2005 floods.
Germany
The reported economic losses in Germany, at about EUR 185 million, were low relative to Switzerland and Austria. Southern Bavaria was most affected. Rivers in the catchments of the Iller, Lech, Loisach, and Isar rivers reached flows of 1-in-100 years and up to more than 1-in-500 years in some locations. New flow records were established at a fifth of the river gauge stations, although total rainfall amounts in the region were lower than in 1999. These new extremes were related to exceptionally steep rising flood waves within a few hours, caused by extreme rainfall amounts within just 12 hours on already saturated soils. Some regions were completely cut off by the floods.
In the aftermath, the Bavarian and German governments refocused efforts on the "flood protection program 2020" that had been proposed after the floods in 1999 and approved in 2001. This program contains measures for new flood defenses, new flood retention basins, the relocation of levees, and the improvement of early warning systems. The 2005 events also revived discussions about obligatory insurance in Germany for natural hazards, similar to Switzerland where they are covered by fire insurance policies.