Offshore islands amplify, rather than dissipate, a tsunami’s power

A long-held belief that offshore islands protect the mainland from tsunamis turns out to be the exact opposite of the truth, according to a new study.

Common wisdom — from Southern California to the South Pacific — for coastal residents and scientists alike has long been that offshore islands would create a buffer that blocked the power of a tsunami. In fact, computer modeling of tsunamis striking a wide variety of different offshore island geometries yielded no situation in which the mainland behind them fared better.

Instead, islands focused the energy of the tsunami, increasing flooding on the mainland by up to 70 percent.

“This is where many fishing villages are located, behind offshore islands, in the belief that they will be protected from wind waves. Even Southern California residents believe that the Channel Islands and Catalina will protect them,” said Costas Synolakis of the USC Viterbi School of Engineering, a member of the multinational team that conducted the research.

The research was inspired by a field survey of the impact of the 2010 tsunami on the Mentawai Islands off of Sumatra. The survey data showed that villages located in the shadow of small offshore islets suffered some of the strongest tsunami impacts, worse than villages located along open coasts.

Subsequent computer modeling by Jose Borrero, adjunct assistant research professor at the USC Viterbi Tsunami Research Center, showed that the offshore islands had actually contributed to — not diminished — the tsunami’s impact.

Synolakis then teamed up with researchers Emile Contal and Nicolas Vayatis of Ecoles Normales de Cachan in Paris; and Themistoklis S. Stefanakis and Frederic Dias, who both have joint appointments at Ecoles Normales de Cachan and University College Dublin to determine whether that was a one-of-a-kind situation, or the norm.

Their study, of which Dias was the corresponding author, was published in Proceedings of the Royal Society A on Nov. 5.

The team designed a computer model that took into consideration various island slopes, beach slopes, water depths, distance between the island and the beach, and wavelength of the incoming tsunami.

“Even a casual analysis of these factors would have required hundreds of thousands of computations, each of which could take up to half a day,” Synolakis said. “So instead, we used machine learning.”

Machine learning is a mathematical process that makes it easier to identify the maximum values of interdependent processes with multiple parameters by allowing the computer to “learn” from previous results.

The computer starts to understand how various tweaks to the parameters affect the overall outcome and finds the best answer quicker. As such, results that traditionally could have taken hundreds of thousands of models to uncover were found with 200 models.

“This work is applicable to some of our tsunami study sites in New Zealand,” said Borrero, who is producing tsunami hazard maps for regions of the New Zealand coast. “The northeast coast of New Zealand has many small islands offshore, similar to those in Indonesia, and our modeling suggests that this results in areas of enhanced tsunami heights.”

“Substantial public education efforts are needed to help better explain to coastal residents tsunami hazards, and whenever they need to be extra cautious and responsive with evacuations during actual emergencies,” Synolakis said. More

 

 

 

Explaining Extreme Events of 2013

A report released today investigates the causes of a wide variety of extreme weather and climate events from around the world in 2013. Published by the Bulletin of the American Meteorological Society, “Explaining Extreme Events of 2013 from a Climate Perspective (link is external)” addresses the causes of 16 individual extreme events that occurred on four continents in 2013. NOAA scientists served as three of the four lead editors on the report.

Of the five heat waves studied in the report, human-caused climate change was found to have clearly increased the severity and likelihood of those events. On the other hand, for other events examined like droughts, heavy rain events, and storms, fingerprinting the influence of human activity was more challenging. Human influence on these kinds of events—primarily through the burning of fossil fuels—was sometimes evident, but often less clear, suggesting natural factors played a far more dominant role.

“This annual report contributes to a growing field of science which helps communities, businesses and nations alike understand the impacts of natural and human-caused climate change,” said Thomas R. Karl, L.H.D., director of NOAA’s National Climatic Data Center. “The science remains challenging, but the environmental intelligence it yields to decision makers is invaluable and the demand is ever-growing.”

Confidence in the role of climate change about any one event is increased when multiple groups using independent methods come to similar conclusions. For example, in this report, five independent research teams looked at specific factors related to the record heat in Australia in 2013. Each consistently found that human-caused climate change increased the likelihood and severity of that event. However, for the California drought, which was investigated by three teams from the United States, human factors were found not to have influenced the lack of rainfall. One team found evidence that atmospheric pressure patterns increased due to human causes, but the influence on the California drought remains uncertain.

When human influence for an event cannot be conclusively identified with the scientific tools available today, this means that if there is a human contribution, it cannot be distinguished from natural climate variability.

“There is great scientific value in having multiple studies analyze the same extreme event to determine the underlying factors that may have influenced it,” said Stephanie C. Herring, PhD, lead editor for the report at NOAA’s National Climatic Data Center. “Results from this report not only add to our body of knowledge about what drives extreme events, but what the odds are of these events happening again—and to what severity.”

The report was edited by Herring, along with Martin P. Hoerling, NOAA’s Earth System Research Laboratory; Thomas Peterson, NOAA’s National Climatic Data Center, and Peter A. Stott, UK Met Office Hadley Centre and written by 92 scientists from 14 countries. View the full report online (link is external).

Also, view the slides for the media briefing on the “Explaining Extreme Events of 2013 from a Climate Perspective” report. More

 

Leaders sign historic sustainable energy & climate resilient treaty

September 2: Over 150 delegates and members of the international development community from more than 45 countries were stunned to see leader after leader approach the podium to sign a historic sustainable energy and climate resilient treaty that will significantly change the lives and destiny of over 20 million small islanders, for the better.

Led by the Deputy Prime Minister of Samoa, Hon. Fonotoe Nuafesili Pierre Lauofo, multiple leaders from the Pacific, Caribbean and African, Indian Ocean and Mediterranean Sea (AIMS) regions, forcefully raised their voices in unison and accepted responsibility for fulfilling the commitment to the Small Island Developing States (SIDS) Sustainable Energy mechanism – SIDS DOCK. The opening for signature of this historic SIDS DOCK Treaty – a SIDS-SIDS Initiative – was a major highlight of the first day of the United Nations (UN) Third International Conference on SIDS, taking place in Apia, Samoa, from 1-4 September.

The unprecedented and unexpected number of Heads of State and Government present, sent a strong signal to the standing room only audience, the SIDS population and the international community, demonstrating how deeply committed SIDS leaders are and that they all firmly believe that SIDS must, have and will take responsibility for charting the future of their countries towards a path that would see a total transformation of the SIDS economy away from fossil fuels, to that of one driven by low carbon technologies. The event was considered so important to the Republic of Cabo Verde, that the Prime Minister, Hon. José Maria Neves, excused himself and his entire delegation from the Plenary Hall, to ensure that Cabo Verde, a SIDS DOCK Founding Member was well-represented at the signing – the Cabo Verde Government has one of the most ambitious plans in SIDS, that aims to achieve 100 penetration of renewable energies in Cabo Verde, by 2020.

More than half the members of the Alliance of Small Island States (AOSIS) were present for the signing of the historic treaty, witnessed by the SIDS DOCK partners Denmark, Japan and Austria, whose kind and generous support facilitated SIDS DOCK start -up activities; also present were SIDS DOCK partners, the United Nations Development Programme (UNDP), the World Bank, the United Nations Industrial Development Organization (UNIDO) and the Clinton

Foundation. The treaty was signed by the governments of Barbados, Belize, Bahamas (Commonwealth of the), Dominica (Commonwealth of), Cabo Verde (Republic of), Cook Islands, Dominican Republic, Fiji (Republic of), Grenada, Guinea Bissau, Kiribati (Republic of), Niue, Palau (Republic of), Saint Kitts and Nevis, Saint Vincent and the Grenadines, Samoa (Independent State of), Seychelles (Republic of), and Tuvalu.

The Statute will remain open for signature in Apia, Samoa until September 5, and will reopen for signature in Belmopan, Belize, from September 6, 2014 until it enters into force. Belize is the host country for SIDS DOCK, with Samoa designated as the location for the Pacific regional office. More

 

 

 

Greenland ice loss doubles from late 2000s

A new assessment from Europe’s CryoSat spacecraft shows Greenland to be losing about 375 cu km of ice year.

The team has produced elevation models for the ice sheets

Added to the discharges coming from Antarctica, it means Earth’s two big ice sheets are now dumping roughly 500 cu km of ice in the oceans annually.

“The contribution of both ice sheets together to sea level rise has doubled since 2009,” said Angelika Humbert from Germany’s Alfred Wegener Institute.

“To us, that’s an incredible number,” she told BBC News.

In its report to The Cryosphere journal, the AWI team does not actually calculate a sea-level rise equivalent number, but if this volume is considered to be all ice (a small part will be snow) then the contribution is likely to be on the order of just over a millimetre per year.

This is the latest study to use the precision altimetry data being gathered by the European Space Agency’s CryoSat platform.

The satellite was launched in 2010 with a sophisticated radar instrument specifically designed to measure the shape of the polar ice sheets.

The AWI group, led by senior researcher Veit Helm, has taken just over two years’ worth of data centred on 2012/2013 to build what are called digital elevation models (DEMs) of Greenland and Antarctica, and to asses their evolution.

These models incorporate a total of 14 million individual height measurements for Greenland and another 200 million for Antarctica.

When compared with similar data-sets assembled by the US space agency’s IceSat mission between 2003 and 2009, the scientists are able then to calculate changes in ice volume beyond just the CryoSat snapshot.

Negative shifts are the result of surface melting and ice discharge; positive trends are the consequence of precipitation – snowfall.

Greenland is experiencing the biggest reductions in elevation currently, losing about 375 cu km a year (plus or minus 24 cu km per year), with most of the action occurring at the west and south-east coast of the continent.

Significant thinning is seen also in the North East Greenland Ice Stream (NEGIS).

“This has three outlet glaciers and one of these, the Zachariae Isstrom, has retreated quite a bit and some volume loss has already been reported. But we see now that this volume loss is really propagating to upper areas, much further into the interior of the ice sheet than has been recorded before,” explained Prof Humbert.

In Antarctica, the annual volume loss is about 128 cu km per year (plus or minus 83 cu km per year).

As other studies have found, this is concentrated in the continent’s western sector, in the area of the Amundsen Sea Embayment.

Big glaciers here, such as Thwaites and Pine Island, are thinning and retreating at a rapid rate.

Some thickening is seen also, such as in Dronning Maud Land, where colossal snowfalls have been reported. But this accumulation does not offset the losses occurring in West Antarctica.

A British-led group recently reported its own Antarctica DEM, using a different algorithm to process the numbers in the CryoSat data.

The AWI outcomes look very similar, and the German team has transferred the exact same approach to Greenland so it can have confidence in comparing the two continents.

The losses also look consistent with the analysis coming out of the American Grace mission, which uses a different type of satellite to monitor gravity changes in the polar regions – to, in essence, weigh the amount of ice being dumped into the sea.

Prof Andy Shepherd, who was part of the British group that reported its findings in May, commented: “This is yet another exciting result from CryoSat, thanks to the team at AWI, charting yet more new ground by providing the first complete survey of ice volume changes in Greenland.

“However, the increased ice losses that have been detected are a worrying reminder that the polar ice sheets are still experiencing dramatic changes, and will inevitably raise concerns about future global sea-level rise.” More