Floods | Destructive floods are increasing in Central Europe, but the opposite is happening in Southern Finland, the researcher says

Climate is changing so that the kind of destructive floods that used to be seen maybe once in a hundred years, now happen maybe once in 20 years or once in 10 years. This is what a researcher at the Finnish Environment Institute thinks Harri Myllyniemi.

According to Myllyniemi, the increase in large floods in Central Europe can be seen from flood observations. For example, in Vienna, Austria, observations of the level of the Danube’s surface have been recorded since the middle of the 19th century.

The flood caused by storm Boris, which raged in Central Europe, is the third largest of the measurements made in Vienna. It is about ten percent smaller than the largest recorded flood of all time, which was in 2013. Four of the ten largest floods in Vienna have occurred in the 2000s.

Harri Myllyniemi, is the flood caused by storm Boris actually normal or does it just seem so huge because we see big floods so rarely?

“There are maybe both here. This is rare. There are recurrences of 50 or 100 years and even more in some large area. This means that flooding happens so rarely on average,” Myllyniemi answers.

“But it’s kind of confusing that in 2002 and 1997 there were even bigger floods in the same areas, which are estimated to be much rarer. As the climate warms, situations that were previously very rare will become more and more common.”

What causes additional flooding?

“As the climate warms, there is more energy in the atmosphere. When the atmosphere is warmer, it is able to bind more moisture. As a result, the big rains are getting bigger and bigger.”

Myllyniemi thinks that it is not yet possible to sigh that the floods caused by Boris are over. In the mountains, the floods have subsided at the top of the rivers, but flood waters are still reaching the lower reaches of the rivers.

To floods can be prepared with flood embankments and levees, but floods cannot be completely prevented. Floods can be tried to be taken into account by zoning in new construction areas, but then it is usually about the water that has rained in the area in question and not, for example, a drastic rise in the level of the river.

“Zoning can affect new residential areas, but not old ones, where it is more difficult to drain stormwater,” Myllyniemi says.

Myllyniemi reminds that there is a difference between Finland and Central Europe, because in Central Europe water cannot spread over a wide area like in Finland. In this case, the water rises higher.

in Finland floods are caused by melting snow in the spring.

“In Lapland, these floods are estimated to increase in the coming decades, but in southern Finland, for example, they will decrease because snowy winters are decreasing in the south. In southern Finland, spring floods are decreasing and have already decreased. When there is little snow, there is no such thing as a flood.”

Myllyniemi says that floods due to heavy rains are increasing, however. Climate warming will intensify heavy rains in Finland as well.

“It has been estimated that the biggest heavy rain floods will increase by 20-25 percent. Such floods that happen in the immediate vicinity and are not caused by a river flowing further away.”

However, heavy rain floods are very local phenomena and do not extend over a wide area. They can be curbed, for example, with stormwater retention basins that slow down the flow of water.

Myllyniemi does not believe that people will be at the mercy of floods in the future.

“When you think about how many people live in the area of ​​the floods caused by Boris, then in that sense it has been done quite well.”