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Weather or climate change?

Irene QuaileJune 6, 2013

Many regions of Germany, and other parts of Central Europe, have been hit severely by flooding in the wake of unusually heavy rain. Climate scientists say climate change may well play a role.

Floods in Dresden. Photo: Michael Kappeler/dpa
DresdenImage: picture-alliance/dpa

The flooding that is creating havoc in so many parts of Germany is primarily caused by a Mediterranean low, according to climate scientist Mojib Latif from the Helmholtz Center for Ocean Research in the German Baltic city of Kiel. This is a weather pattern that develops over the Mediterranean, sucks in masses of water and travels around the Alps before moving in from the East over Poland and the Czech Republic to Germany.

There are two main reasons why the weather resulted in such extreme flooding, according to Gerhard Lux, a meteorologist at the German Meteorological Office.

"First, we had a very wet May," Lux told DW. "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."

The experts stress that weather events are always individual events, which cannot be directly attributed to a changing climate.

However, analysis of German weather trends - data which is available going back to 1871 - indicates an increase in severe rainfall events, said climate expert Latif.

Rescue workers ride a boat in the flooded streets of the east German town of Bad Schandau after the Elbe river has broken its banks, June 5, 2013. REUTERS/Thomas Peter (GERMANY - Tags: DISASTER ENVIRONMENT)
The river Elbe has flooded Bad Schandau in eastern GermanyImage: Reuters

"If we look back over the past few decades, heavy rainfall seems to be occurring twice as often as was the case 100 years ago," he said.

Gerhard Lux was less confident about the relying on the statistics, arguing that an increase in severe rainfall is not as easy to demonstrate as the obvious rise in temperature. Nevertheless, looking at climate models, he also expects an increase in heavy rain as the planet warms.

Climate scientist Stefan Rahmstorf of the Potsdam Institute for Climate Impact pointed readers of his blog to studies looking at the increase in extreme weather events during the last decade. He wrote that recent analyses indicated that the rise in emissions of greenhouse gases was linked to a rise in extreme events.

"Even if the weather remained unchanged in other respects and we only had the warming, we would have to expect heavier precipitation whenever masses of air are saturated with water and it gets rained off," he wrote.

'Once in a century' events no longer

There is a clear physical explanation for the connection between precipitation and warmer temperatures, said Mojib Latif.

"Water content in the air depends on the temperature as temperature regulates how much water can evaporate," he explained. "The water is then released as precipitation and comes back down to earth. The higher the temperature, the more water can evaporate and the higher the potential for heavy rain."

The term "flood of the century," used in Germany to describe the last bout of dramatic flooding in the country in 2002, is no longer appropriate, Latif added.

"In the 1990s we had 'once-in-a-century' floods. Then we had them again in 2002, and now in 2013 we are seeing the same again," he said. "What used to happen once in a century could well become an event that recurs every decade or so."

A worker prepares an area on the river Oder for flooding. Photo: Patrick Pleul dpa/lbn
The protective dyke has been shifted to give the river Oder more spaceImage: picture-alliance/dpa

Protection against extreme weather?

Gerhard Lux stressed that the weather forecasters were able to predict the heavy rain. The problem, he said, was preparing to cope on the ground.

"That requires a certain infrastructure. And that always poses the question of how to prepare for an event that happens every few years?"

Indeed, Mojib Latif warned against putting off investments in flood protection.

A house is partially submerged by flood water in the centre of the Austrian village of Emmersdorf, about 100 km (62 miles) west of Vienna June 3, 2013. Torrential rain in Tyrol, Salzburg, Upper and Lower Austria caused heavy flooding over the weekend, forcing people to evacuate their homes. REUTERS/Leonhard Foeger (AUSTRIA - Tags: DISASTER ENVIRONMENT)
Flooding will occur more frequentlyImage: Reuters

"These floods have demonstrated once again that we have not adapted as best we could. One thing we will probably have to do is return some of what we have taken away from nature. We need more natural flood planes, for instance. And we will have to consider unpopular measures like building bans in risk areas."

The experts argue that adaptation to climate change is unavoidable, given the continuing rise in CO2 emissions.

"We have not taken any action to halt climate change, in spite of all the climate conferences," said Latif. "And even if we did manage to stabilize CO2 emissions and reduce them in the long term - and there is no sign of that at the moment: It will take decades before we can change course. That means in the coming decades, we just have to live with the fact that extreme rainfall and flooding will happen more often."