|April 08--The Intergovernmental Panel on Climate Change, a Nobel Prize-winning group of scientists from across the world, said it is likely that heavy rainfall events will become more frequent in three areas of the globe: the polar regions, the tropics and the northern mid-latitudes in winter. |
Its report, released on March 28, was written by 220 scientists from 62 countries and deals with managing risks from extreme weather.
Warm air can hold more moisture so the world will get more rain, "but the critical fact here is that this rainfall increase is not evenly distributed," Tim Flannery writes in "The Weather Makers," a 2005 book about climate change.
Flannery, a biologist who has taught at Harvard, said air pollutants such as carbon dioxide, other greenhouse gases and ozone have pushed up the tropopause, a barrier between the two lowest levels of the atmosphere and the place where much of earth`s weather is generated.
While the stratosphere above it cools and shrinks, the troposphere, the level closest to the surface, expands and heats under a lid of greenhouse gases.
"By warming the troposphere, we both change the weather patterns globally and increase the likelihood of extreme weather events," Flannery writes.
He cites a powerful El Nino of 1997-98, the European heat wave of 2003 and the "one of the worst storm seasons ever experienced in Florida" in 2004. Hurricane Katrina hit the next year, when the book was published.
The International Panel on Climate Change report said the scientists have low confidence that the number of tropical cyclones -- which are called hurricanes in the northern latitudes -- will increase. Wind speed and rainfall of hurricanes, however, are likely to increase, the report said.
While predicting more rainstorms in some areas, the report said scientists have medium confidence that droughts will become more frequent and more intense in regions, including southern and central Europe, central North America, Mexico and southern Africa.
The report rates as very likely the chances that heat waves will become more frequent and intense over most land. Also, the scientists are virtually certain that the number and intensity of warm days and nights will increase globally.
To describe intense rainfall, like Hurricane Irene and Tropical Storm Lee, the U.S. Geological Survey computes the likelihood that those storms will strike in various parts of the nation.
One benchmark that engineers use is whether their controls for stormwater will withstand the worst flood expected in 100 years.
While the term 100-year flood has grown common, it becomes confusing when severe storms occur just a few years or even a few weeks apart.
"I think we`ve all heard people say `How can we have two, 100-year storms in five years?" which is a great example of the mass confusion presented by this attempt at labeling storms," Jim Brewster of the National Weather Service in Binghamton, N.Y., said by email.
Instead of referring to 100-year storms, Brewer and other scientists prefer saying such floods have a 1 percent chance of occurring in any given year.
So were Hurricane Irene and Tropical Storm Lee 100-year storms that arrived 10 days apart?
It depends on the location.
The 7.49 inches of rain that fell on Sept. 7, 2011, with the arrival of Tropical Storm Lee near Binghamton exceeded the rain expected in the kind of storm that has a 1 percent chance of occurring in any year.
Brewster said rainfall from Hurricane Irene probably passed that mark in parts of the Catskills, too, but not in Northeastern Pennsylvania.
The 3.23 inches recorded at the Wilkes-Barre/Scranton International Airport in Avoca on Aug. 28, 2011, would be expected every five to 10 years, he said.
During Tropical Storm Lee, the total of 4.09 inches of rain measured between Sept. 6 and 7, 2011, also fell within the 5- to 10-year range.
Looking through the records back to 1901 for Northeastern Pennsylvania, the closest that Brewster found to a 100-year storm was Sept. 27, 1985. That day 5.98 inches of rain fell, an amount predicted every 80 to 90 years.
(c)2012 The Standard-Speaker, Hazleton, Pa.
Distributed by MCT Information Services
Story Image: Irene`s rain floods out Route 100 in Waitsfield, Vt on Aug. 28, 2011. Sandy Macys, AP
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