AIR: major flooding in Southern and Central Germany

AIR Worldwide, the catastrophe modelling firm, has reported that communities across southwestern Germany experienced major flooding last weekend, following several days of heavy rainstorms that impacted a broad swath of Europe.

On Sunday, more rain fell in a few hours than the region normally experiences over several weeks. Further significant flooding was reported in south eastern Germany on Wednesday.

Consistent with what AIR has observed in previous events, including the 2002 floods, it expects much of the loss from this event to occur outside the floodplain. Smaller claims from off-floodplain losses can add up to a significant portion of total insured losses.

It has been reported that several thousand people were directly affected by the floods in Lower Bavaria. A state of emergency was declared in the districts of Rottal-Inn and Passau. For the Rott River—a tributary of the Inn—the highest flood warning stage was declared, with very high water levels possible at some stations. In Triftern, in the district of Rottal Inn, Bavaria, the Altbach Creek exceeded the highest water levels in the last 25 years. Widespread thunderstorms are forecast to prevail until Friday.

According to AIR, in Germany, a stationary upper-level low pressure system, with a surface low named Elvira, has caused significant hail and heavy rainfall from strong thunderstorms.

Rainfall totals from Sunday 30 May through Monday 31 May ranged from 100 to 150 mm in the regions hit hardest. Rainfall amounts in excess of four inches fell in two hours in some regions of southwest Germany, namely the region of Schwaebisch Hall in the north of Baden-Württemberg.

The low pressure system remained stalled over Germany due to the jet stream, which led to additional flooding. The synoptic situation resulted in a strong contrast between cool dry air in the north and west of Germany with warm moist air over the south and east.

It was over this region and along this boundary where strong thunderstorms with heavy rainfall were continuously spawned. In the Baden-Württemberg region, a mesoscale convective system developed, allowing heavy rainfall to persist throughout the evening traversing from the northwest to southeast, and resulting in rainfall totals of 100-150 mm across that area.

Those dynamics combined with the slow movement resulted in favourable conditions for disastrous flooding across the region. Since low pressure gradients prevailed over Germany, the thunderstorms moved very slowly or were quasi-stationary concentrating their precipitation on confined areas.

Up to 67 mm of rain in one hour was measured near Landshut (Bavaria) and 124 mm over 24 hours in Neuenstadt am Kocher (District Heillbronn). Lightning injured more than 30 people in Germany and France and killed a man in southern Poland. Discharges measured at the Neckar tributaries Kocher and Jagst went from below average to 10- to 75-year flood levels in as little as two to six hours.

Already on Friday 27 May, Baden-Wuerttemberg and Bavaria experienced thunderstorms and large hail. Heavy precipitation in the state of Hesse flooded some basements; a layer of hail up to 20 cm accumulated.

Thunderstorms across southern and central Germany on Saturday 28 May flooded basements. Hail up to 5 cm in diameter was reported in southern Bavaria, and a 10 cm hail layer accumulated; 33 people were injured by a lightning strike at a soccer match.

Sunday 29 May saw major flash floods in Baden-Wüerttemberg, Bavaria, and Hesse; additional flooding occurred in the Rhineland-Palatinate and Hesse on Monday May 30 and in Lower Bavaria on June 1.

While local floods have been reported over the weekend across southern and central Germany, the greatest destruction appears to have been experienced in Schwaebisch Gmuend.

AIR said the worst flash flooding occurred in the small town of Braunsbach on the slopes of a narrow valley on the Kocher River. A fast moving torrent of water swept through the town and piled debris up to two or three meters high. Streets were choked with debris including mud, cars, boulders, and trees. In addition to the flash flooding there was flooding on the valley bottom, where gauges went from below average to 10- to 75-year water levels in a matter of hours. The banks of two streams were reportedly breached.

The Kocher flows into the Neckar, the 10th largest river in Germany, on which shipping was temporarily suspended as levels rose above the bank full stage.

The flooding occurring on Wednesday in Lower Bavaria along the Inn and its tributaries caused severe damage to buildings, cars, and infrastructure. At least four houses reportedly have collapsed or have been carried away. Flooded transformer stations caused power and communication outages.

According to AIR, about 90% of single-family homes in Germany are of masonry construction, with the remainder typically wood; a few are reinforced concrete. The presence of a cellar increases the risk for contents damage, although heavily used cellars often have better flood defences than unfinished ones. Apartment buildings are generally of masonry and reinforced concrete. Commercial buildings are typically of masonry or, in some cases, reinforced concrete. Note that many buildings in the region have mixed occupancies, with the ground floor used for shops while the upper floors are residential.

AIR has said of all the natural hazards that cause property damage in Europe, flood is the most costly. Flooding is a regular occurrence—one not limited to the coast or low-lying river valleys, but nearly ubiquitous due to off-floodplain flash flooding. Damage data from recent flood events in Germany indicate that a significant portion of flood losses come from off-floodplain locations, often at a considerable distance from large rivers and their floodplains.

The average flood insurance take-up rate for residential buildings across Germany is estimated at around 38 percent. However, there are significant regional differences in insurance. There is no nationwide compulsory insurance coverage for flood, and it is typically excluded from standard residential, commercial, and industrial policies. The exception is Baden-Württemberg, where most building policies include flood coverage. The take-up rate in Baden-Württemberg is 95 percent, but in neighbouring Bavaria it is only 27 percent.