Hurricane Kyrill rages across Europe

With wind speeds of over 200 kilometres per hour, Kyrill raged across Europe during the night on Friday. Peak values of the hurricane were measured on the Feldberg in the Black Forest and on the Brocken in the Harz mountains. 47 people died in the hurricane, many were injured. The damage is estimated to be in the billions.

It was the worst hurricane since Lothar: Kyrill uprooted trees, covered roofs and smashed cars. Several people were killed by falling trees, and over a hundred were injured. The power grid collapsed in many regions. At Berlin’s main railway station, gale-force winds tore a piece of iron weighing several tonnes from the façade. The station had to be evacuated, but no one was injured. All over Germany, the fire brigade and police were in constant action, and disaster alerts were issued in many places.

At times, rail traffic had to be completely suspended. Overhead lines were defective, fallen trees blocked the tracks. Kyrill also completely disrupted air and shipping traffic. The hurricane hit the German North Sea coast less badly than expected, and the feared storm surge did not occur. In contrast, the forest in North Rhine-Westphalia suffered severe devastation. Millions of trees were blown down or torn out of the ground, roots and all. Kyrill also left a trail of destruction in Great Britain, France and the Netherlands.

On Friday morning, the authorities gave the all-clear, the storm and storm surge warnings were lifted. After the hurricane chaos, the clean-up work is now in full swing.

Storms of the century Kyrill and Lothar

The images are the same: forests shaved bare, electricity pylons knocked down, cars crushed. In December 1999, hurricane Lothar swept across Central Europe even more violently than Kyrill. Especially in northern France, Switzerland, southern Germany and Austria, Lothar reached top speeds of 270 kilometres per hour and caused the worst storm damage: 110 people died; in total, more than 6 billion US dollars worth of damage was caused. And now, with Kyrill, another storm of the century?

Climate researchers suspect that climate change will cause such violent winter storms to occur even more frequently in the future. The storms that sweep across Europe in the winter months originate in the North Atlantic. The warming of the oceans now ensures that more water evaporates there. This in turn favours the formation of hurricane lows like Lothar and Kyrill.

Hurricane Katrina devastates US coast and New Orleans

It is one of the worst natural disasters in the United States. On Monday morning (29 August 2005), Hurricane Katrina reached the American Gulf Coast. At 280 kilometres per hour and accompanied by torrential rain, the tropical cyclone hit the coast and the city of New Orleans.

People, cars and houses were simply swept away by Katrina’s gales. The US states of Florida, Alabama, Georgia, Mississippi and Louisiana suffered severe damage from the hurricane. The city of New Orleans, however, with its nearly 500,000 inhabitants, was hit the worst. In the afternoon, the levees of the city, which is partly below sea level, broke at 150 metres. The water masses shot into the city centre and flooded a good 80 percent of the area. Entire residential areas are now completely under water. Due to the power cuts, however, the floodwaters cannot be pumped out. An airport is also flooded and had to be closed. Many access roads are closed – New Orleans is almost completely cut off from the outside world. Although rescue efforts are in full swing, disaster control is completely overwhelmed. The city is drowning in brackish water and chaos. Looting and violence have already been reported.

Warnings about the storm came too late for many. Only a good million people were able to leave the New Orleans area in time. Thousands of people who were unable to flee are now stranded in the Louisiana Superdome football stadium, hoping that the waters will soon recede. It is not yet known how many people lost their lives as a result of Katrina. Damages in the billions are expected.

Where did Katrina come from?

A tropical storm developed over the Bahamas on 23 August, which meteorologists named “Katrina”. The storm grew into a hurricane and moved over the southern tip of Florida on 25 August, killing nine people. Over land, Katrina weakened slightly. Shortly after reaching the Gulf of Mexico, however, Katrina picked up speed again and became a hurricane once more. Katrina reached its maximum strength and hit the southern coast of Louisiana on the morning of 29 August with winds of 280 km/h. This made it one of the most severe hurricanes ever to hit Louisiana. This made it one of the most severe storms ever recorded in the Gulf of Mexico – with devastating consequences. Even meteorologists had not expected such a destructive force.

Deadly tornado

A tornado leveled the small town of Joplin in the US state of Missouri on Sunday. More than 100 people were killed, hundreds were injured and many are still missing. The tornado swept right through the town, aerial photos show a ten-kilometre-long and one-kilometre-wide path of devastation.

The storm caused severe damage in many areas of Missouri, but Joplin was the worst hit: three quarters of the town of 50,000 people are in ruins. The tornado covered roofs and tore entire buildings to pieces. Houses, churches, supermarkets and petrol stations were heavily damaged or completely destroyed. A seven-storey hospital was badly hit and its medical equipment was hurled up to a hundred kilometres away. Due to the danger of collapse, the hospital was evacuated and patients were taken to emergency shelters. Rescue efforts are further complicated by the loss of power and telephone networks. Relief workers report a tremendous amount of destruction. Three quarters of the city have been practically wiped out.

Residents were warned of the storm too late: because the tornado was shrouded by rain and hail, its destructive power could not be predicted. Jay Nixon, Governor of Missouri, has now declared a state of emergency for the region. Warnings of further severe weather in Missouri have been issued.

The Tornado Road

More than 1,000 tornadoes pass through the USA every year. Between 500 and 600 of the feared tornadoes alone take the route of the notorious “tornado alley”. The “tornado alley” runs through the US states of Texas, Oklahoma, Kansas and Nebraska. There, conditions are particularly favourable for tornadoes: warm, humid air rising over the Gulf of Mexico meets dry, cold air from the north unhindered in the plains of the Great Plains. Violent thunderstorms are formed here, from which many tornadoes develop. However, not only the United States of America, but also Germany counts a few of the dreaded tornadoes each year. But because the Alps prevent warm, humid air masses from the Mediterranean region from reaching us, tornadoes are much rarer here.

Wind strength and wind speed

If smoke can rise vertically and there is hardly a breath of air, then there is no wind. In a hurricane, on the other hand, the wind is so violent that it carries even heavy objects with it. Wind can vary in strength – and the strength of the wind is indicated in the “Beaufort scale”, which ranges from wind force 0 with complete calm to a hurricane with wind force 12.

The scale is named after the British Sir Francis Beaufort, who used a similar scale a good 200 years ago. At that time, wind strength was determined, for example, by observing the height of the waves on a ship or the effect of the wind on the sails and then reading off the corresponding wind strength in a table. Today, each wind force has a specific wind speed. Wind force 0, for example, means that the wind is blowing less than one kilometre per hour. This means that it is imperceptible – there is no wind. If, on the other hand, the wind is blowing at a speed of 39-49 kilometres per hour, i.e. almost as fast as a car in the city, then large branches are already moving. Such a strong wind has a wind force of 6. When the wind speed exceeds 62 kilometres per hour, it is called a storm. And a hurricane is on its way when the wind speed exceeds 118 kilometres per hour: This corresponds to the highest value on the scale, wind force 12. In this case, severe devastation is to be expected.

Incidentally, the strongest wind ever measured on the earth’s surface blew across Barrow Island in Western Australia in April 1996 at a whopping 408 kilometres per hour. Such a violent storm can blow railways off their tracks and cause buildings to collapse like houses of cards. The storm also brought terrible devastation to Barrow Island.

Cyclones

In August 2005, the southeast of the USA experienced a catastrophe: Hurricane Katrina raced along the coast, killing almost 2000 people. Like all hurricanes, Katrina was a tropical cyclone. In other regions of the world they are also called typhoons or cyclones. Storm surges, torrential rain, landslides and floods are their consequence. But how does such a cyclone come about?

A hurricane forms where warm water evaporates and warm humid air rises fast and high. To compensate, cold air is sucked down. A thunderstorm moves in. Due to the Coriolis force, the cold and warm air masses begin to rotate as if in a spiral. As they rotate, they suck in even more warm, humid sea air. In this way, the cyclone becomes stronger and stronger: it can reach a diameter of several hundred kilometres and travel thousands of kilometres. Its air masses reach speeds of up to 300 kilometres per hour. Only in the centre is there no wind: this is the eye of the hurricane. It can take more than a week for the storm to subside.

To form such a cyclone, the water must have a temperature of at least 27° Celsius. In addition, the Coriolis force is needed, which causes a rotation of the air masses. Towards the poles the water is too cold, towards the equator the Coriolis force becomes too low. For this reason, hurricanes only form in a strip in the tropics that lies roughly between latitudes 5 and 20 degrees.

Smaller, but much faster than hurricanes are tornadoes, also called “whirlwinds”. They form in hot, humid regions when warm and cold air meet during a thunderstorm. They descend from a thundercloud to the ground like a huge trunk. Inside this proboscis, there is very low air pressure, which sucks in the air masses and swirls them around. Such tornadoes can be very small, but they can also reach a diameter of up to 1.5 kilometres and are clearly visible from afar because they sweep dust and water vapour far upwards. After a short time, the spook is over.

Where the tornado races along, however, it leaves a trail of destruction. The dangerous air vortexes are particularly common in the Midwest of the USA. There is even a real “tornado road” there: Because cold and warm air masses from the north and south collide here unhindered, several hundred tornadoes race through this area every year.

The consequences of climate change

Climate change is already particularly visible in the polar regions. Just a few decades ago, the Arctic Ocean was largely covered by ice. But due to rising temperatures, this ice cover is melting: in the last 30 years, its area has almost halved. At the same time, the ice cover is becoming thinner and thinner. Climate researchers have calculated that the ice could melt completely in the next 20 years. Sea levels would rise by several metres as a result. But not only the ice sheets at the poles are melting. The glaciers in the high mountains are also losing mass.

Because the sea level is rising due to the melting of the ice, ever larger coastal areas are being flooded. Low-lying island states, such as the Maldives in the Indian Ocean or Tuvalu in the Pacific, are therefore increasingly threatened by storm surges. And not only the sea level, but also the water temperature is rising with climate change. As a result, more water evaporates and more water vapour is stored in the air. This increases the greenhouse effect, which heats up the atmosphere even more. In addition, this increases the risk of storms such as heavy rain and hurricanes.

In dry regions, deserts are spreading due to rising temperatures. More and more droughts are causing rivers to dry up and previously green areas to wither. In the south of Spain, for example, the usual rainfall that is urgently needed for agriculture has been absent for years. And the water shortage in southern Europe continues to worsen.

All these consequences of climate change can already be observed now. Climate researchers are trying to calculate how it will continue with the help of computer models. But the future is difficult to predict because so many influences determine our climate. For example, the melting of glaciers dilutes the salty sea water with fresh water. The salinity of the sea, however, drives ocean currents. So what could happen if the lower salinity causes the warm Gulf Stream to break off? Would it then first become colder instead of warmer in Europe? What would happen if the permafrost thaws in the far north? Will tonnes of the greenhouse gas methane then escape from the ground? And will this accelerate climate change?

So far, no one can answer that exactly. But with all the unanswered questions, one thing seems certain: If we do not drastically reduce our carbon dioxide emissions, temperatures on this globe will continue to rise.