Extreme Precipitation and Scary Math

BY BRUCE E. JOHANSEN

By 2011, scientific studies were beginning to bear out what many incidents of extreme precipitation have been telling weather watchers who follow the meteorological news: a warmer atmosphere produces more rain and snowfall—and a greater risk of damaging floods. These studies also lend credence to a scary prospect, and one that popular media coverage of these studies largely missed: while increases in temperature are linear, intensity of precipitation increases exponentially. One must wonder what the atmosphere has in store for us once temperature increases get really serious. 

"Climate models have improved a lot since ten years ago, when we basically couldn't say anything about rainfall," said Gabriele Hegerl, a climate researcher at the University of Edinburgh. Hegerl and colleagues compiled data from weather stations in the Northern Hemisphere, then compared it with precipitation models. The study covered the years 1951 through 1999. 

A second study associated damaging floods in 2000 in England and Wales with temperature increases. Myles Allen of the University of Oxford and colleagues found that human-induced climate change “may have almost doubled the risk of the extremely wet weather that caused the floods.” 

While increases in extreme precipitation have been recognized on an incident-by-incident basis for more than ten years, these studies provide systematic evidence. "What has been considered a 1-in-100-years event in a stationary climate may actually occur twice as often in the future," said Allen. 

Hegerl and colleagues wrote in Nature: “We show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas… Changes in extreme precipitation projected by models, and thus the impacts of future changes in extreme precipitation, may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming.” 

The study of flooding in the UK said: “The UK floods of October and November 2000 occurred during the wettest autumn in England and Wales since records began in 1766. These floods damaged nearly 10,000 properties across that region, disrupted services severely, and caused insured losses estimated at £1.3billion.” 

World-wide Wake-up Call 

The wake-up call has become worldwide. Warm air holds more water, and the atmosphere is about five percent moister than 40 years ago, a factor in the increasing severity of deluges. Where it isn’t raining, more heat provides faster evaporation, increasing drought. 

An organization containing meteorologists from 189 countries said in August, 2010 that the summer’s heat waves, droughts, and floods displayed global warming’s effects. "Several diverse extreme weather events are occurring concurrently around the world, giving rise to an unprecedented loss of human life and property. They include the record heat wave and wildfires in the Russian Federation, monsoonal flooding in Pakistan, rain-induced landslides in China, and calving of a large iceberg from the Greenland ice sheet," said the World Meteorological Organization (WMO). 

In January, 2011 near-record floods swept a large area of northeastern Australia, including Brisbane, a city of two million people, forcing evacuation of 30,000 homes and businesses and killing at least 15 people. At the same time, floods rampaged through towns near Rio de Jaineiro, Brazil, killing more than 600 people, most of them in landslides. Many were killed in their beds during the wee hours of the morning, including at least 250 in Teresoplis.  

A Rare Deluge in India

As floods devastated Pakistan in the summer of 2010, an extremely rare deluge inundated the town of Leh, in Ladakh, India, which sits in what is usually one of the driest deserts on the planet. The village sits in what is a high-altitude desert protected from most precipitation by surrounding mountains. The average rainfall there in August is 15 millimeters—a fraction of an inch. In the early morning of August 6, 2010 however, a half-hour deluge swept much of the village away, killing 150 people, with several hundred missing. The storm was so intense, and isolated, that it missed a weather station in the valley, and went unmeasured. 

In 2010, during July and August, Pakistan mourned the deaths of more than 2,000 people in its worst monsoon deluge on record. One-fifth of the country was flooded by the raging Indus River, and 20 million people were affected; eight million were driven from their homes. The floods followed record high temperatures; the 129 F. reading there in July was the highest ever recorded anywhere in Asia. 

During the fall of 2010, Colombia experienced its worst rainy season in at least 30 years, leaving more than 130 people dead and a million homeless. Also during 2010, by the end of July, 1,072 people were killed by floods in China, according to Shu Qingpeng, deputy director of the Office of Flood Control and Drought Relief, with the central government. About 140 million people were affected by floods in China during those seven months; a million homes had been destroyed, and economic damage was estimated at $31 billion. 

The Rio Negro, a major Amazon tributary, went from record high to record low levels between 2009 and 2010—a severe deluge-drought cycle. An Associated Press report said that: “Floating homes along the Rio Negro now rest on muddy flats, and locals have had to modify boats to run in shallower waters in a region without roads. Some riverbanks have caved in, although no injuries have been reported. Enormous fields of trash and other debris have been revealed by the disappearing waters. The drought is hurting fishing, cattle, agriculture and other businesses, prompting authorities to declare a state of emergency in nearly 40 municipalities.” 

REFERENCES 

Allan, Richard P. “Climate Change: Human Influence on Rainfall.” Nature 470(February 17, 2011):344-445. 

Min, Seung-Ki, Xuebin Zhang, Francis W. Zwiers, and Gabriele C. Hegerl. “Human Contribution to More-intense Precipitation Extremes.” Nature 470(February 17, 2011):378-381. 

Pall, Pardeep, Tolu Aina, Dalthi A. Stone, Peter A. Stott, Toru Nozawa, Arno G. J. Hilberts, Dag Lohmann, and Myles R. Allen. “Anthropogenic Greenhouse Gas Contribution to Flood Risk in England and Wales in Autumn 2000.” Nature 470(February 17, 2011): 382-385. 

Schiermeier Quirin. “Increased Flood Risk Linked to Global Warming; Likelihood of Extreme Rainfall May Have been Doubled by Rising Greenhouse-gas Levels.” Nature 470 February 17, 2011, 316. 

http://www.nature.com/news/2011/110216/full/470316a.html

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May 2nd 2011

Larry Gardner - A man who is not afraid of the sea will soon be drowned -Synge