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Europe’s flood risk may double by 2050

March 2, 2014 in Europe, European Union, Extreme weather, Flooding, Weather Systems

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Floods submerge St Mark's Square in Venice: The prospect is for worse to come Image: Wolfgang Moroder via Wikimedia Commons

Floods submerge St Mark’s Square in Venice: The prospect is for worse to come
Image: Wolfgang Moroder via Wikimedia Commons

By Tim Radford

As much of Europe recovers from the severest winter in several centuries, scientists say average annual flood losses could be almost five times greater by mid-century.

LONDON, 2 March – The catastrophic floods that soaked Europe last summer and the United Kingdom this winter are part of the pattern of things to come. According to a new study of flood risk in Nature Climate Change annual average losses from extreme floods in Europe could increase fivefold by 2050. And the frequency of destructive floods could almost double in that period.

About two thirds of the losses to come could be explained by socio-economic growth, according to a team led by Brenden Jongman of the University of Amsterdam in the Netherlands and Stefan Hochrainer-Stigler of theInternational Institute for Applied Systems Analysis in Austria.

That is because more development and investment means there is more at risk from any flooding. But the other third of the increase will be delivered by climate change, and a shift in rainfall patterns in Europe.

From 2000 to 2012, floods in European Union countries averaged €4.9 billion (US $6.8 bn) a year in losses. In the floods of June 2013, losses tipped €12 bn (US $16.6 bn) in nine countries of Central and Eastern Europe. The annual average losses could increase to €23.5 bn (US $32.4 bn) by 2050.

Unprecedented floods like those of 2013 occur on average once every 16 years now. By 2050, the probability will have increased to once every 10 years.

Floods widespread

The team looked at monthly peak river discharges in more than 1,000 river sub-basins to begin making their estimates: they also matched these peak flows with atmospheric circulation patterns. The point of the study was to deliver more accurate information.

“We brought together expertise from the fields of hydrology, economics, mathematics and climate change adaptation, allowing us for the first time to comprehensively assess continental flood risk and compare the different adaptation options,” said Brenden Jongman.

And Dr Hochrainer-Stigler said the new study for the first time accounted for the correlation between floods in different countries. Risk-assessment models tended to consider river basins as independent entities. “But in actuality, river flows across Europe are closely correlated, rising and falling in response to large-scale atmospheric patterns that bring rains and dry spells to large regions.”

All of this points to greater strains on the pan-European Solidarity Fund that finances recovery from disaster within the European Union. “If the rivers are flooding in Central Europe, they are also likely to be flooding in eastern European regions,” he said. – Climate News Network

Offshore wind could calm hurricanes

February 26, 2014 in Climate, Coastal Threats, Energy, Extreme weather, Hurricanes, Technology, USA, Weather Systems, Wind power

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It's smaller, but the same principle applies: Wind energy is dissipated as it crosses a wind farm Image: By Michael via Wikimedia Commons

It’s smaller, but the same principle applies: Wind energy is dissipated as it crosses a wind farm
Image: By Michael via Wikimedia Commons

By Tim Radford

US scientists say that very large wind farms could not only withstand a hurricane: they would also weaken it and so protect coastal communities.

LONDON, 26 February – US engineers have thought of a new way to take the heat out of a hurricane. Fortuitously-placed offshore wind farms could make dramatic reductions in wind speeds and storm surge wave heights.

Hurricanes are capricious consequences of peculiar sea temperature and wind conditions, while wind farms are the outcome of years of thoughtful design and investment, and not an emergency response to a severe weather warning.

But, according to new research in Nature Climate Change, a giant wind farm off the coast of New Orleans in 2005 could have lowered the wind speeds of Hurricane Katrina by between 80 and 98 miles an hour, and decreased the storm surge by 79%.

Katrina was a calamitous event that caught civic, state and federal authorities off-guard, and devastated the city. But an array of 78,000 wind turbines off the coast would, according to Mark Jacobson of Stanford University, and Cristina Archer and Willett Kempton of the University of Delaware, have defused its force dramatically – and turned a lot of hurricane energy into electricity at the same time.

Wind turbines turn in the wind to generate energy. The laws of thermodynamics are inexorable, so a national grid’s gain is the wind’s loss, because wind energy is dissipated as it crosses a wind farm. One turbine literally takes the wind out of the sails of another.

Tempest models

One of the three Nature Climate Change authors, Cristina Archer, last year examined the geometry of a hypothetical wind farm to work out how to place turbines most efficiently to make the best of a gusty day, rather than have one bank of turbines turning furiously while the others barely stir.

But this same translation of wind circulation to electrical circuitry suggested another accidental consequence. Mark Jacobson and his colleagues used sophisticated computer models to test the impact of a hurricane on a wind farm, and since the US has both cruel experience and highly detailed records of hurricane events, he and his Delaware partners decided to model three notorious tempests: Superstorm Sandy, which slammed into New York in 2012 and caused $82 billion damage in three US states, Hurricane Isaac, which hit Louisiana the same year, and Hurricane Katrina in 2005.

“We found that when wind turbines are present, they slow down the outer rotation winds of a hurricane,” Professor Jacobson said. ”This feeds back to decrease wave height, which reduces movement of air toward the centre of the hurricane, increasing the central pressure, which in turn slows down the winds of the entire hurricane and dissipates it faster.”

And Cristina Archer put it more vividly: “The little turbines can fight back the beast,” she said. Her colleague Willett Kempton added: “We always think about hurricanes and wind turbines as incompatible. But we find that, in large arrays, wind turbines have some ability to protect both themselves and coastal communities from the strongest winds.”

Double benefit

The conclusions are based entirely on computer simulations. Real world tests are for the moment unlikely, chiefly because wind farms tend to have dozens or, at the most, hundreds of turbines and the hurricane experiment was based on turbines in their tens of thousands, delivering hundreds of gigawatts.

But Professor Jacobson and Dr Archer tend to think big anyway. They argued in 2012 that four million wind turbines in the world’s windiest places could generate at least half the world’s electricity needs by 2030 without interfering too greatly with global atmospheric circulation.

The tempest-taming qualities of really big wind farms would deliver an added bonus: they could offer protection to vulnerable coastal cities. The costs of wind-farming on such a scale would be huge, but then the losses to coastal cities from flooding and storm damage in a rampant climate change scenario are expected to rise to $100 trillion a year by 2100.

The three authors calculate that the net cost of such projects – after considering all the good things that could come from them – would be “less than today’s fossil fuel electricity generation net cost in these regions and less than the net cost of sea walls used solely to avoid storm damage.”

A sea wall to protect one city might cost anything from $10 billion to $29 billion, and that is all it would do: protect that city. A really big wind farm would offer protection during cyclones, typhoons or hurricanes and generate carbon-free energy all year round. – Climate News Network

Warming ‘will double extreme El Niños’

January 20, 2014 in Climate, El Niño, Extreme weather, Ocean Warming, South America, Warming, Weather Systems

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A NOAA vessel services a buoy used to measure ocean temperatures and provide warning of El Niños Image: Courtesy of NOAA/US Dept of Commerce

A NOAA vessel services a buoy used to measure ocean temperatures and provide warning of El Niños
Image: Courtesy of NOAA/US Dept of Commerce

By Tim Radford

Rising global temperatures are likely to double the frequency of the most severe El Niños, the periodic atmospheric disruptions which affect weather in much of the world.

LONDON, 20 January – An El Niño is part of a natural cycle: a huge blister of heat in the equatorial Pacific, usually around Christmastime, that periodically triggers unseasonal floods in the western US, and extreme heat and forest fires in the Indonesian rainforest and the Australian bush.

It happens and seems to have happened through human history. It has nothing to do with global warming or climate change. Except this: according to the latest study by climate scientists in Australia, the US, China and Britain, global warming is likely to make the most extreme El Niño events happen twice as frequently.

Since an El Niño episode is characterised by – the scientists say in Nature Climate Change – “severely disrupted global weather patterns, affecting ecosystems, agriculture, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide,” this is unlikely to be welcome news.

Right now, and for the past year, conditions in the equatorial Pacific have been neither unusually warm nor unusually cool. There is no El Niño right now. But for two summers running, even without help from unusual Pacific conditions, Australia has been hit by record temperatures and appalling forest fires, so the news is ominous.

Wenju Cai of Australia’s CSIRO marine and atmosphere research and colleagues report in the journal that extreme El Niño events tend to happen when sea surface temperatures higher than 28°C develop in the normally cool and dry eastern Pacific, to trigger big shifts in the atmospheric convection zones (areas of instability caused by temperature differences), and climate models show that these episodes have normally occurred every 20 years or so.

Profound impact

Now, as carbon dioxide levels rise and the global average temperatures creep up, these extreme events are likely to be twice as frequent: every decade or so.

The last extreme event, in 1997-98, caused an estimated $35 billion (US dollars) in damage and claimed an estimated 23,000 lives worldwide. It also made 1998 the hottest year ever in average global temperatures, a record that lasted for more than a decade.

“The question of how global warming will change the frequency of extreme El Niño events has challenged scientists for more than 20 years. This research is the first comprehensive examination of the issue to produce robust and convincing results”, said Mike McPhaden of the US National Oceanic and Atmospheric Administration, one of the co-authors.

The authors warn that potential future changes in such extreme events could have “profound socio-economic consequences.” They conclude: “With a projected large increase in extreme El Niño occurrences, we should expect more occurrences of devastating weather events, which will have pronounced implications for twenty-first century climate.” – Climate News Network

Worse cyclones will hit East Asia

January 16, 2014 in China, Coastal Threats, Extreme weather, Japan, Korea, Ocean Warming, Weather Systems

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Tacloban in the Philippines, November 2013: East Asia stands to be worse hit by cyclones Image: Trocaire from Ireland via Wikimedia Commons

Tacloban in the Philippines, November 2013: East Asia stands to be worse hit by cyclones
Image: Trocaire from Ireland via Wikimedia Commons

By Kieran Cooke

Hundreds of thousands of people in the Philippines are trying to piece together their lives after the devastation caused late last year by tropical cyclone Haiyan. New research shows that while such cyclones are growing in strength they are increasingly tracking northwards to hit the coasts of China, Korea and Japan.

LONDON, 16 January – It will be of little comfort to people in the southern and central Philippines repeatedly hit by tropical cyclones over the years, but a new study indicates that storm patterns might be shifting northwards.

The study, by a team of scientists at Seoul National University and other South Korean scientific institutions, looks at tropical cyclone activity across the north-west Pacific between 1977 and 2010.

Researchers found that increasing sea surface temperatures likely due to climate change, together with changes in atmospheric circulation patterns, have led to a significant increase in the intensity of tropical cyclones hitting the east Asia region over the 30-year period.

“Noticeable increases of greenhouse gases over the globe could influence rising sea surface temperature and change large-scale atmospheric circulation in the western North Pacific, which could enhance the intensity of tropical cyclones hitting land over east Asia”, says Professor Chang-Hoi Ho, one of the study’s authors.

Intensity changes

The study, which appears in the journal Environmental Research Letters, analyses five separate sets of data relating to the growth and behaviour of tropical cyclones across the north-west Pacific.

It found that the area of maximum storm intensity had shifted both westward and northward: while the intensity of tropical cyclones had lessened somewhat in areas of south-east Asia it had increased significantly in east Asia – particularly in coastal regions of central China and of Japan and around the Korean peninsula.

The study found that cyclones were tending to build up around the northern Philippines and track along coastal areas from Vietnam northwards, gaining energy along the way.

The researchers say a significant factor behind the alteration in the intensity and direction of tropical cyclones is a change in what’s called the Walker circulation – an ocean-based atmospheric circulation system over the Pacific.

Sea temperature difference

The Walker circulation strengthens as the difference between sea temperatures in the warmer western Pacific and the colder central-eastern Pacific grows more marked: the result is that wind flows associated with the Walker circulation drive tropical cyclones towards the north-eastern coast of Asia, where they reach maximum intensity.

“This change in large-scale climatic fields suggests that the principal region in which many tropical cyclones attain peak intensity during their lifetime might have been translocated”, says the study.

Cyclone Haiyan ravaged a large part of the central coastline of the eastern Philippines. However, the study found that over the 30-year period analysed, tropical cyclone activity in seas off the east Philippines coast had decreased while “the maximum intensity has shifted toward east Asia and intensified landfall intensity.”

That’s bad news for millions of coastal dwellers in central and northern China, Japan and on the Korean peninsula. More catastrophic tropical cyclones will strike east Asia in future than ever before, says the study. – Climate News Network

Arctic melting ‘affects temperate zones’

December 18, 2013 in Arctic, Extreme weather, Polar ice, Weather, Weather Systems

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Bear on the ice near Svalbard: Arctic warming appears to be having effects far to the south Image: Hannes Grobe via Wikimedia Commons

Bear on the ice near Svalbard: Arctic warming appears to be having effects far to the south
Image: Hannes Grobe via Wikimedia Commons

By Tim Radford

Weather extremes in temperate countries may be the consequence of the melting of Arctic snow and ice, according to Chinese and American scientists.

LONDON, 18 December – The shrinking Arctic sea ice – a loss of 8% per decade during the last 30 years – isn’t just bad news for polar bears. It could be bad news for citizens of Europe and the United States who like to think they live in a temperate zone.

Qiuhong Tang of the Chinese Academy of Sciences and colleagues from Beijing and the US report in Nature Climate Change that they have identified a link between declining snow and ice in the polar north, and catastrophic heat waves, droughts and floods in the mid-latitudes.

Recent years have been marked by devastating extremes of heat in Russia, Europe and the US, and by unprecedented floods in the UK and in East Asia. Over the same period, snow cover and sea ice in the Arctic have been in retreat.

The link, the scientists say, could be changes in atmospheric circulation triggered by the loss of snow cover.

There are perfectly good reasons to expect some impact on weather systems from a retreat of the snow line. In the first place, snow and ice are white – that is, they reflect sunlight, and its warmth – while ocean and forest and tundra are dark, and absorb heat.

Closer link established

Good snow fall means lots of soil moisture in the summer months while dry ground tends to be warmer. So temperatures change, overall. Air currents flow because of pressure differences, which are linked to temperature. So winds would inevitably be affected.

But the researchers went beyond this loose generalisation, to match satellite observations of the snow cover and sea ice extent in the Arctic with atmospheric data, to explore the effects further south.

They found a distinct set of patterns of circulation associated with the loss of snow and ice.

The upper atmospheric winds in the north become weaker, and the jet stream shifts northwards, which means that weather systems become more stable. The longer a weather system stays in one location, the greater the probability that the conditions will become extreme.

In 2012, in the continental United States, it was the hottest summer ever recorded and the second worst for floods, hurricanes and droughts. In September 2012, the Arctic sea ice fell to its lowest level ever. It could be just chance, it could be just two aspects of the same big picture, but Tang and colleagues think not.

Hotter future

They think the link is clear. They even see a closer link between the loss of sea ice and a change in circulation pattern, even though the area of sea ice lost is only half of the total area of snow lost in the months of May and June.

That could be because much of the northern hemisphere snow cover is over land which is forested anyway – that is, partly dark – whereas the Arctic sea can only be white or dark.

The link is not certain – they are putting the idea out there for others to challenge or confirm, which is the way science advances – but the three authors argue that their research builds on studies by others which spell out the same conclusion.

And they don’t see things getting better, either for polar bears who need the sea ice to hunt, or for farmers in the great plains of the US or city dwellers on floodplains and river estuaries in the temperate world.

“As greenhouse gases continue to accumulate in the atmosphere and all forms of Arctic ice continue to disappear, we expect to see further increases in summer heat extremes in the major population centres across much of North America and Eurasia where billions of people will be affected”, they conclude. – Climate News Network