It's not your imagination: North Jersey is getting warmer and wetter and the flooding on at least some rivers is getting worse, experts say.

Though these conclusions do not fully explain the weird weather -- a 70-degree January day, 8 inches of rain and severe flooding in April -- they validate people's suspicion that the weather is getting more unpredictable, if not more extreme.

In the last 12 months, the state has experienced the wettest fall and April on record and the warmest November and December on record, according to New Jersey State Climatologist David A. Robinson.

Robinson cautions that although computer models and historical data show a warming trend, it's too early to say if the extreme weather will become the new norm.

"People are so quick to jump on every extreme weather event and say, 'Look! Look! Look!' " Robinson said. "We need to wait for more data, more information or more extreme extremes."

An Aug. 7 report on extreme weather by the United Nations' World Meteorological Society has added to the debate over whether extreme events are more frequent globally.

The report, by the U.N.'s Intergovernmental Panel on Climate Change, claimed that the past 50 years saw an increasing trend in extreme events and stated it is "very likely that hot extremes, heat waves and heavy precipitation events will continue to become more frequent."

At the local level, researchers from Montclair State University's Passaic River Institute have confirmed the popular belief that flooding is getting more extreme in the Hackensack and Passaic river basins.

Institute Director Kirk R. Barrett and his colleagues studied 18 U.S. Geological Survey gauges that had been in place for at least 50 years and found that at least 10 of the gauges showed that 100-year floods - events that have a 1 percent chance of happening in any given year - were getting more severe.

"The flood that used to be the 100-year flood many years ago is now more common than that," Barrett said of his unpublished report, which he has presented at two conferences.

Researchers did not study the cause of the increased flooding, but Barrett said it could be due to a combination of development in the river basins, which reduces the amount of soil that can soak up rain, and increased rainfall.

Barrett's study squares with Oakland homeowner Jamie Willis's experience.

Willis said her home on the Ramapo River, which was included in Barrett's study, has flooded three times in the last 2½ years, most recently during April's nor'easter.

Last week, she showed off the water lines on the cinderblock wall in her basement.

"This is from April 2007," she said, pointing to a gray line 3 feet up the wall.

The floods of April and October 2005 were lower down on the wall, and the line from Tropical Storm Floyd, which caused major floods in September 1999, was 6 feet up.

Willis believes the 400-home Ramapo River Reserve development less than half a mile from her house may have had an impact. A U.S. Army Corps of Engineers project to increase the river's capacity through Oakland also worsened flooding in the area temporarily.

Still, the recent precipitation and temperature increases in North Jersey - 10 counties, including Bergen and Passaic -- have been significant.

The average yearly precipitation between 1971 and 2000 increased by more than 5 inches over the average from the 75 previous years, while temperatures in the same period increased by .3 degree Fahrenheit over historical norms, according to state climatology data.

Increases since 2001 have been more marked -- and if they continue, it could mean trouble for towns such as Wayne, which sits in the Passaic River Basin at the confluence of several rivers.

Wayne Mayor Scott Rumana said he has noticed an increase in flooding and heavy rainstorms as the years have gone by. But he said the town doesn't need scientific confirmation to know that it has to take action to prevent more disastrous flooding.

The town is part of the Central Passaic River Basin task force, which is considering buying property in flood-prone areas and engineering solutions.

"Inaction is the unacceptable position," Rumana said.

Mayors such as Rumana will likely have to make decisions without the guidance of scientific evidence for a while yet.

Rutgers University Professor Alan Robock said global warming changes the chances that extreme weather will happen. But climate study requires large amounts of data and no one can attribute a storm, or a month of warm weather, to any one factor.

"People have been telling me that there's weird weather my entire career as a meteorologist," said Robock, who got his Ph.D. 30 years ago.