The last time a "once-in-a-lifetime" flood swamped the tri-state area was 1993 -- less than a lifetime ago for most people.

"We had floods in 1993, 2001 and now in 2008," said Steve Kuhl, meteorologist in charge at the Quad Cities office of the National Weather Service. "It is certainly true this flood is historic -- especially along the Cedar and Iowa rivers. Now, we're expecting the Mississippi River from Muscatine south to approach 1993 levels."

Is there a possible link between global climate change and increased frequency of local flooding?

"I'm surprised more people aren't asking this question," said Jim Angel, state climatologist with the Illinois State Water Survey. "We had the floods in 1993, and here -- 15 years later -- we have another big flood."

Harry Hillaker, Iowa's state climatologist, said a possible climate change link "is one of those things where if you asked 100 climatologists that question, you would probably get 100 different answers.

"I think with any kind of weather event or seasonal event -- and this is really a seasonal event because it built up over time -- it is always next to impossible to determine a particular cause," Hillaker said. "You can say the weather pattern was like this and the jet stream was like that, but why is it like that? The short answer is 'who knows?'"

Dr. Vaughan Turekian, chief international officer for the American Association for the Advancement of Science that publishes the journal Science, said that although it is difficult to pin the blame for single events -- such as the tri-state area floods -- on climate change, "the flooding and large amounts of rain are consistent with what scientists believe will happen more often with global warming."

Turekian said the amount of water vapor in the atmosphere likely would increase.

"The atmosphere would have the capacity to hold more water, so when it rains, it rains harder," he said.

Local rains have been falling with increased frequency this year. On the heels of the snowiest winter on record, the tri-state area has been on the receiving end of rainfall during the third-wettest spring.

"The above-average snowfall had put a lot of water into the system," Kuhl said. "Earlier rains in April caused flooding, and the soil was totally saturated and the rivers were running bank-full. When we got into this pattern in May, with this heavy rain, the weather pattern was locked in for three weeks."

The tri-state area then began tapping into a tropical air mass.

"We had Gulf of Mexico moisture for three weeks," Kuhl said.

The atmosphere became unusually saturated for this time of year.

"When upper-level disturbances moved through the area, it triggered heavy rain," Kuhl said. "The area rivers just couldn't take any more rain."

Whether the wetter-than-usual pattern definitely marks a climate shift, Angel said, is difficult to deduce based on the relatively limited amounts of available, reliable climate data.

"We only have 150 years of rainfall data," Angel said. "Even when people say 'it's a 500-year flood,' that really is just a guess," Angel said.

Hillaker said the past 50 years in Iowa have been wetter than the previous 50 years.

"But if you go back beyond 100 years ago, from the 1840s to early 1880s, the data is more sketchy, but that appears to be another wet period," Hillaker said.

Determining the extent of such climate change depends on analyzing such trends.

"With climate change, you have to look at the long term," Angel said. "If we're starting to get this (flooding) every 15 years, then you have a greater degree of confidence that it would be evidence of climate change, because that would point to trends."