A warming world will further intensify extreme precipitation events

April 4, 2013

Heavy precipitation.

According to a newly-published NOAA-led study in Geophysical Research Letters, as the globe warms from rising atmospheric concentrations of greenhouse gases, more moisture in a warmer atmosphere will make the most extreme precipitation events more intense.

The study, conducted by a team of researchers from the North Carolina State University’s Cooperative Institute for Climate and Satellites-North Carolina (CICS-NC), NOAA’s National Climatic Data Center (NCDC), the Desert Research Institute, University of Wisconsin-Madison, and ERT, Inc., reports that the extra moisture due to a warmer atmosphere dominates all other factors and leads to notable increases in the most intense precipitation rates.

Percent maximum daily preciptation difference (2071-2100) - (1971-2000).

Download here (Credit: NOAA)

The study also shows a 20-30 percent expected increase in the maximum precipitation possible over large portions of the Northern Hemisphere by the end of the 21st century if greenhouse gases continue to rise at a high emissions rate.

“We have high confidence that the most extreme rainfalls will become even more intense, as it is virtually certain that the atmosphere will provide more water to fuel these events,” said Kenneth Kunkel, Ph.D., senior research professor at CICS-NC and lead author of the paper.

The paper looked at three factors that go into the maximum precipitation value possible in any given location: moisture in the atmosphere, upward motion of air in the atmosphere, and horizontal winds. The team examined climate model data to understand how a continued course of high greenhouse gas emissions would influence the potential maximum precipitation. While greenhouse gas increases did not substantially change the maximum upward motion of the atmosphere or horizontal winds, the models did show a 20-30 percent increase in maximum moisture in the atmosphere, which led to a corresponding increase in the maximum precipitation value.

Rainy day.

The findings of this report could inform “design values,” or precipitation amounts, used by water resource managers, insurance and building sectors in modeling the risk due to catastrophic precipitation amounts. Engineers use design values to determine the design of water impoundments and runoff control structures, such as dams, culverts, and detention ponds.

“Our next challenge is to translate this research into local and regional new design values that can be used for identifying risks and mitigating potential disasters. Findings of this study, and others like it, could lead to new information for engineers and developers that will save lives and major infrastructure investments,” said Thomas R. Karl, L.H.D., director of NOAA’s NCDC in Asheville, N.C., and co-author on the paper.

The study, Probable Maximum Precipitation (PMP) and Climate Change, can be viewed online.

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Tepco: radiation from Fukushima plant declines further (Reuters)

TOKYO (Reuters) – The operator of Japan's tsunami-hit Fukushima nuclear power plant Monday said the amount of radiation being emitted from the complex has halved from a month ago, in the latest sign that efforts to bring the plant under control are progressing.

The Fukushima Daiichi plant, 240 kilometers (150 miles) northeast of Tokyo, was damaged in March by a devastating earthquake and tsunami in the world's worst nuclear accident since the Chernobyl disaster 25 years ago.

"Our latest measurements show that radiation from the damaged reactors is 100 million becquerels per hour, which is one eight-millionth of the amount measured soon after the accident," Tokyo Electric Power's (Tepco) vice president Zengo Aizawa told reporters during a monthly review.

Aizawa said that this translates to about 0.2 millisievert per year of radiation measured at the fringes of the plant, below the 1 millisievert safety limit according to government guidelines.

The amount is half of what Tepco announced at its review a month ago.

In light of the progress being made in cooling its damaged reactors, which suffered nuclear fuel meltdowns in the first days of the crisis, Tepco formally brought forward its plan to bring the plant to a state of "cold shutdown" within this year, instead of by January as initially planned.

It had said last month it was hoping to achieve a cold shutdown within the year but had not made a formal declaration.

Technically, a cold shutdown is a state in which water used to cool nuclear fuel rods remains below 100 degrees Celsius, preventing the fuel from reheating.

With the help of newly built cooling systems, Tepco's efforts to cool the reactors have progressed steadily, with temperatures at all three of the damaged reactors falling below 100 degrees late in September.

But despite this development, Tepco and the government have been cautious about immediately declaring a cold shutdown.

"We still need to proceed with care. We need to continue monitoring whether the temperatures of the reactors and radiation levels being emitted remain stable going forward," Yoshinori Moriyama, deputy director-general of the government watchdog Nuclear Industrial and Safety Agency, told the same news conference.

Declaring a cold shutdown will have repercussions well beyond the plant as it is one of the criteria the government said must be met before it begins allowing about 80,000 residents evacuated from within a 20 km (12 mile) radius of the plant to go home.

Japan faces a massive cleanup task if these residents are to be returned home -- the environmental ministry says about 2,400 square km (930 square miles) of land surrounding Daiichi may need decontamination, an area roughly the size of Luxembourg.

Even if a cold shutdown is declared Tepco has acknowledged that it may not be able to remove the fuel from the reactors for another 10 years and that the cleanup at the plant could take several decades.

It also has to decontaminate tens of thousands of tonnes of contaminated water pooled at the plant, a result of its efforts to cool the reactors early in the crisis by pumping in vast amounts of water, much of it from the ocean.

(Reporting by Shinichi Saoshiro; Editing by Sanjeev Miglani)

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Japan's TEPCO admits further reactor meltdowns (AFP)

TOKYO (AFP) – The operator of Japan's tsunami-hit Fukushima nuclear power plant on Tuesday said it believed fuel had partially melted inside three reactors, as long suspected by experts.

Tokyo Electric Power Company (TEPCO) said new readings on water gauges indicated that the fuel had dropped to the bottom of the containment vessels of units two and three, matching its earlier assessment of unit one.

In all three reactors, relatively low temperatures indicated that the fuel was now mostly covered by water that has been pumped into the vessels, meaning there was no immediate threat of an uncontrolled full meltdown.

"It is highly possible that (partial) meltdowns have occurred at reactors two and three," a TEPCO spokesman said as the firm released its latest analysis of data from the plant after the March 11 quake and tsunami.

"Most of the fuel is believed to have fallen to the bottom (of pressure vessels that contain fuel rods) as has happened in reactor one," he said. "They are now being cooled and are in stable conditions."

Japan's March 11 disaster, which left nearly 25,000 people dead or missing, knocked out cooling systems at the Fukushima plant. This led reactors to overheat, triggering the worst nuclear crisis since Chernobyl 25 years ago.

Reactors four, five and six were under maintenance when the quake hit.

TEPCO estimates it will bring all six reactors to safe "cold shutdown", with low pressure and low temperatures, by some time between October and January, although it will take far longer to dismantle the plant.

Emergency crew have sprayed water into the facility since the quake to cool down the reactors and keep fuel rods in containment pools submerged under water, creating tonnes of toxic runoff that has leaked into the Pacific.

This week TEPCO warned that containment vessels for the radioactive water were almost full.

The company is building a new water treatment facility and has also docked a storage tank called the "megafloat" off the site to hold more low-level contaminated water.

An international panel of nuclear experts arrived in Japan this week to assess the accident and is due to report back to the UN's International Atomic Energy Agency in Vienna in late June.

The IAEA announced last week the mission, headed by Mike Weightman, chief inspector of nuclear installations in Britain, would comprise 20 experts from 12 different countries.

Japan has also decided to set up a panel independent of the nuclear industry and bureaucracy, and mostly made up of academics, to look into the causes of the crisis. It is expected to compile a mid-term report in December and a final report by mid-2012.

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