"If we look at precipitation events over the long term, there is an increase in frequency of extremes. Events such as the one we're seeing now are occurring about twice as often as they did a century ago," said climate scientist Mojib Latif from the Helmholtz Center for Ocean Research in the German Baltic city of Kiel.
Extreme events, points out Latif, are not limited to floods. Nor are they limited by geography.
"Weather is unpredictable," said Latif. "But what we are seeing from the scientific data is instability, and not just in Europe." Africa, for example, has experienced severe flooding in the past few years with tens of thousands displaced. And extreme events are not limited to flooding.
"Drought conditions are increasing as well as flood conditions," said Latif. "We're going to be seeing many more extremes in both directions in the future. They are two sides of the same coin."
The cause of the present flood has to do with the mass of water vapor in the air, which is partly the result of higher air temperature. "The water content in the air depends on the temperature, as temperature regulates how much water can evaporate," said Latif.
The European flooding of the past few weeks was caused by a low-pressure system over eastern Europe drawing warm, moist air from the Mediterranean region. The warm water vapor concentrated north of low-lying mountain ranges and the Alps, and then condensed when it arrived in the cooler regions of central and eastern Europe. The result was torrential rainfall.
Where there are cities, there will be floods
Areas where the ground is sealed at the surface, such as roads and heavily developed urban expanses like plazas and parking lots, are at high risk for flooding. Most cities provide little in the way of a porous layer of earth or sand through which surface water can permeate.
Gerhard Lux, a meteorologist at the German Meteorological Office, told Deutsche Welle: "We had a very wet May. That means we had already seen a lot of precipitation, and the ground was completely saturated. Then we had excessive, heavy rainfall in many areas of Germany in late May and early June. The ground could not absorb it, so it had to flow off on the surface, rapidly filling streams and rivers."
In Prague, areas in the north and south of the city are under water, according to a report in The Financial Times. Metal barriers erected along the Vltava have stemmed the tide in the city's historic center, mitigating flood damage. However, large parts of the Prague underground system remained shut last week, and officials said it would not reopen for days.
Prague's central sewage-treatment plant was shut down on June 3 to prevent damage from the high water. That means sewage from the capital seeps into the river, which as of this weekend was still flooding parts of the city. The city government hopes to restart the plant within a few days.
Although floodwaters in Prague have begun to recede, the German city of Dresden is bracing itself for the river Elbe to rise 16 feet higher than normal. Dresden, whose baroque city center was swamped in the 2002 flood, hopes its remediation efforts after that flood will pay off. The Elbe River, which runs through it, has been rising relentlessly against a barrier of sandbags, and one of the bridges over the river was closed.
Footing the bill
German Chancellor Angela Merkel toured some of the worst-affected areas of flooding in Germany last week and pledged €100 million ($130 million) in immediate federal government aid, Der Spiegel reported.
Merkel was accompanied by Bavarian Gov. Horst Seehofer, who pledged an additional €50 million ($65 million) in regional aid for Bavaria. German Transport Minister Peter Ramsauer said the road and rail network alone had sustained more than €100 million ($130 million) worth of damage. The true cost of damage, he told Deutsche Verkehrs-Zeitung, could not be assessed until the water had receded.