How does land mass affect a typhoon

The future of the cyclones

Reports of destructive cyclones appear to have increased in recent years. But this impression is deceptive, says Christian Herold, forecast meteorologist at the German Weather Service: "In the last few decades there has been no clear trend in terms of the frequency of cyclones." This is mainly due to the fact that the measurement period is relatively short, as hurricanes have only been measured using satellite data for a few decades.

Hurricanes, tropical cyclones in other parts of the world, are characterized by meteorologists based on their intensity. The scale ranges from 1 to 5. This classification indicates the wind speeds at which the storm sweeps across its area, how much precipitation it brings with it and how much damage it causes.

Haiyan reached the destructive force of a hurricane of the highest category at its height. "Such wind speeds as we have now experienced over the Philippines have actually not yet been observed," says Friedrich-Wilhelm Gerstengarbe from the Potsdam Institute for Climate Impact Research. "Haiyan also absorbed a lot of water vapor, so there was very heavy rainfall with flooding."

A tropical cyclone forms over the sea when water at a temperature of at least 26 degrees Celsius evaporates. The water vapor condenses, the air heats up and pulls cooler air up with it. The rotation of the earth causes the airflow to rotate. When the cyclone hits a coast, it releases all of its stored energy over the land masses and lets off steam there.

More intensely than before - or not

All scientists seem to agree that hurricanes have not become more common in the last few decades. But their destructive power has increased, says Gerstengarbe: "There are now more stronger tropical cyclones with levels 3, 4 and 5."

In 2008, researchers led by Thomas Jagger from Florida State University in Tallahassee, USA, wrote in the journal "Nature" that the wind speeds of tropical cyclones over the Atlantic in particular have increased over the past 30 years. Kerry Emanuel from E.O. Lawrence Livermore National Laboratory in California has calculated that the hurricanes over the western northern Pacific in particular have become more destructive in recent years.

Other scientists, on the other hand, cannot observe a trend at all: In the past few decades, hurricanes have caused more damage. But that's simply because insurance values ​​are rising and there were more and more expensive possessions where the hurricane landed. That wrote Roger Pielke jr. from the University of Colorado at Boulder and his colleagues in the 2012 Journal of Climate.

Mojib Latif from GEOMAR - Helmholtz Center for Ocean Research Kiel does not consider it surprising that so many studies come to such different results. In the case of such rare events as hurricanes, the database is simply very poor. He compares the situation to a marked die. "You have to roll the dice very often until you can see whether the dice is marked or not." It is similar with cyclones: if there is a trend, it would take a relatively long time before this trend can also be observed.

Haiyan brought a lot of water with him

Climate change could be to blame

It seems quite possible that hurricanes could become even more powerful in the future. Because the sea is warming up due to climate change. "There are some regions where the ocean temperature has increased significantly: in the Caribbean and also where Haiyan has now emerged," says Barley Sheaf. The water temperature there is now 30 degrees Celsius, previously the water was only 28 degrees.

When the seawater warms up, it provides more drive for a cyclone, explains meterologist Sven Plöger. "The warmer the sea, the more moisture gets into the atmosphere - and that is the energy that is available for the storm." So as the sea temperature rises, so does the possibility of cyclones becoming more intense.

But Christian Herold points out that these are all just models. "The system is very complex. It is not known to what extent a higher sea temperature leads to violent storms - or whether this is overcompensated by other processes," he says. "It could also be that the higher water temperature changes other parameters in the atmosphere that might inhibit the formation of a typhoon."

Hurricanes like Haiyan are unpredictable

Take better precautions

"Haiyan's strength surprised us all," says Mojib Latif. He sees this as an alarm signal. "The question is: do we want to take the risk that the models are right or not?" Climate protection activists are calling for the emission of carbon dioxide to be limited in order to prevent such devastating cyclones.

Early warning systems help in the short term. Meteorologists can now predict hurricanes up to four days in advance. But evacuating an area where so many people live within a very short time is hardly feasible.

Therefore, one must also think about not settling at all in particularly endangered areas, says Plöger. "But we will never have one hundred percent security. In such unbelievable storms there will always be a risk to life and limb."