An aerial view of the flooding in Passau, Germany, 03 June 2013. The floodings in Bavaria continue to worsen. (Peter Kneffel/AP)

Large areas of central Europe are experiencing their worst flooding in decades after heavy rainfall last week pushed rivers beyond their banks.

At least 21 people have died across Germany, Austria, and the Czech Republic, and thousands have been forced to evacuate their inundated homes. Preliminary estimates suggest the flooding has caused several billion dollars in damage.

In Passau, Germany – along the confluence of the Danube and Inn rivers – floodwaters rose to their highest levels in over 500 years. The city declared a state of emergency after swollen rivers cut off outside road access. Soldiers from the German army are being sent to flooded areas in southeastern Germany to provide disaster relief.

In the Czech Republic, the country is on high alert for its most severe flooding since at least 2002. Authorities closed the iconic Charles Bridge in Prague, where the Vltava River is flowing at 10 times its normal volume through the Czech capital, writes the BBC.

Rainfall amounts

Germany’s national weather service reports that southern and eastern Germany experienced near uninterrupted rainfall since Thursday of last week.

The village of Aschau, Bavaria recorded an impressive 405.1 mm of rainfall (15.9 inches) in just four days, of which 6.71” fell in 24 hours. Several new precipitation records were set, including:

  • A monthly record of 157 mm (6.2”) in Hamburg
  • A daily rainfall maximum of 97.3 mm (3.8”) on May 26 in St. Englmar, Bavaria
  • Germany’s second wettest May since 1881

Rainfall has been equally relentless in neighboring Austria, sending torrents of runoff through Alpine streams and rivers. Salzburg, one of the rainiest cities last month, received 259 mm (10.2”) of rain, according to Austria’s meteorological service (ZAMG).

In a press release, the Austrian weather service says that May saw twice the normal monthly precipitation in most of the country’s nine provinces. Nationally, May 2013 ranked among the top 3 wettest Mays in 156 years of records (alongside 1962 and 1965).

Meteorological dynamics

Rainfall totals (in millimeters) recorded across Austria and southeastern Germany, May 30 – June 3. (Austrian Institute for Meteorology and Geodynamics)

An expansive area of low pressure parked over eastern Europe is to blame for the excessive rainfall. Warm, moist Mediterranean air colliding with colder Atlantic air was lifted over the north side of the Alps. A stationary front then formed, bringing an extended period of unsettled weather.

While this pattern setup is not unusual in the central Alps, the amount of precipitation measured in some locations was historically significant.

Alexander Orlik, a climate scientist at Austria’s Institute for Meteorology and Geodynamics (ZAMG), puts this year’s flooding in perspective (in German):

“Statistically speaking, four-day rainfall totals of this magnitude happen every 40 to 70 years…but when we consider that in some places most of this rain fell in just one or two days, then we’re looking at a less than 1 in 100 year event.”

Last week’s rains came at the end of an already cool and wet spring in Austria and most of western Europe. ZAMG notes that the March-May period ended up among Austria’s seven wettest springs on record. Several weeks of above-normal precipitation had already saturated the ground, which forced the additional rainfall to flow away as runoff.

In Germany, the high water table and saturated soil may cause problems for agriculture this summer. In a national analysis of groundwater levels, the German weather service last week announced that ground moisture is at its highest in over 50 years, and in some places near record high levels (see image).

Fortunately, rain-weary residents in central Europe can look forward to drier conditions in the coming days. Rain will start to taper off from west to east as Atlantic high pressure slowly pushes inland. Even so, many areas in central Europe still face a significant flood threat, as floodwaters only slowly start to recede.

Scroll for more photos of the flooding…

Rescuers navigate through an overflooded street in Passau, southern Germany, on June 3, 2013. (Christof Stache/AFP/Getty Images)

A general view shows the flooded centre of Passau, southern Germany, on Monday, June 3, 2013. Raging waters from three rivers have flooded large parts of the southeast German city following days of heavy rainfall in central Europe. (Matthias Schrader/AP)

Traffic signs are flooded at the highway 8 from Munich to Salzburg in Grabenstaett near Traunstein, southern Germany. Raging waters from three rivers have flooded large parts of the southeast German city following days of heavy rainfall in central Europe. (Matthias Schrader/AP)

The land is flooded around Kolbermoor, Germany, 03 June 2013. Heavy rains are causing serious flooding in Bavaria and other areas of Germany. (Peter Kneffel/AP)

Floodwater of the river Mulde encloses some houses north of Eilenburg, eastern Germany. (Jens Wolf/AFP/Getty Images)

A vehicle with sandbags drives on a flooded street in St. Martin in the Austrian province of Salzburg, Sunday, June 2, 2013. (Kerstin Joensson/AP)

A person looks at the heavily damaged road between Lofer and Waidring in the Austrian province of Tyrol, Monday, June. 3, 2013. (Kerstin Joensson/AP)

This photo taken on June 3, 2013 shows the flooded historical main square of Melk, Austria. (Dieter Nagl/AFP/Getty Images)

An aerial view of flood water in the city of Melk, Lower Austria, Austria, 03 June 2013. (Roland Schlager/EPA)

A women crosses a makeshift bridge over overflooded streets in Unterloiben, Austria on June 4, 2013. (Dieter Nagl/AFP/Getty Images)

A traffic sign is partially submerged in flooded street in the village of Sarling in Lower Austria, on June 4, 2013. (Leonhard Foeger/Reuters)

Rescue workers pull a rubber dinghy next to a damaged car in the flooded western Austrian village of Koessen June 3, 2013. (Dominic Ebenbichler/Reuters)

An aerial view shows the submerged church of the village of Pocaply near the town of Litomerice in the Czech Republic. (Petr Josek/Reuters)

A family watches swollen Vltava river in the centre of Prague, Czech Republic, Sunday, June 2, 2013. (Roman Vondrous/AP via CTK)

The statue of spiritual leader Sri Chinmoy was partially submerged in water from the rising Vltava River in Prague Sunday. (David W. Cerny/Reuters)

An aerial view shows the flooded city centre of Grimma, eastern Germany, on June 3, 2013. Parts of the eastern and southern Germany were flooded due to heavy and ongoing rainfall. (Jens Wolf/AFP/Getty Images)