Fed by rain and melting snow, swollen waterways have swamped vast tracts of land in Romania, Bulgaria, Serbia and Hungary this month, driving thousands of people from their homes.

In Romania, the worst-hit country where tens of thousands of hectares are submerged, some 2,800 people moved to high ground overnight after dikes near the southern villages of Bistret, Spantov and Oltina collapsed under the flood water's pressure.

More people were on the move on Monday with furniture and belongings crammed into army trucks, tractors and horse carts, and authorities said some 4,600 in all were expected to flee in the coming hours.

"The water is close to Bistret. We have to evacuate all the villagers this evening," Mayor Constantin Raicea told Reuters.

Soldiers set up tents on higher ground near Bistret to house some 1,000 refugees, but Raicea said most of the 1,600 people evacuated were staying with relatives in neighboring villages.

President Traian Basescu, touring the area, urged local officials to act quickly: "The villagers from Bistret need to be evacuated immediately. We have to evacuate the area using force because some people do not want to leave their houses."

Some 40 km (25 miles) downstream in Bechet, a village of 5,200, rescuers geared up to take more people to safety as another dike crumbled in a nearby village.

"Around 30 families have moved to a neighboring village and we are now going to evacuate some 1,200 people," Bechet mayor Constantin Oclei told Reuters.

Soldiers and civilians built new berms and reinforced existing dikes to protect low-lying settlements in the area.

The floods forced hundreds of Romanians to spend Orthodox Easter Sunday -- a closely observed holiday in the Balkans -- in a bleak refugee camp away from their flooded village with little idea when they would be able to return home.

SLOW RETREAT

Officials said the Danube had receded where it leaves Serbia and enters Romania but there might be more breaches of dikes.

"Water pressure is very high on these earth dikes and there are more in danger of collapse," said Elena Anghel, from Romania's National Hydrology Institute.

In Hungary, more large cracks had appeared by Monday morning in the dikes at the confluence of the Tisza and Koros rivers, where 6,000 soldiers and civilians battled the floods overnight.

Both rivers ebbed very slowly, by around 2 to 8 centimeters (1 to 3 inches) from the peak in the worst-hit area, and there was still pressure on the dikes, state news agency MTI reported.

The Danube originates in Germany and flows through or forms borders with 10 countries before emptying into the Black Sea.

In Bulgaria's Nikopol, a town of 4,000 which is half under water, several families evacuated over the weekend as water flooded their houses. In all, 61 people have fled the village.

"It's really difficult to make a prediction for the coming days," said Georgi Linkov, head of civil defense in Pleven, northern Bulgaria.

"We hope the rains the meteorologists forecast will not be pouring down, because there's a risk of soaking the dikes."

West of Oklahoma City, two tornadoes tore through sparsely populated areas of Canadian County, damaging hangars at the municipal airport south of El Reno.

Television footage showed debris from the buildings being lifted and flung about as the tornado moved overhead. Parts of the hangars' roofs were ripped away and a couple of airplanes were moved outside.

Damage from the storms, which formed near U.S. Highway 81 and Interstate 40 about 40 miles west of Oklahoma City, appeared to be isolated, Lt. Stewart Meyer, an Oklahoma Highway Patrol spokesman said.

Nearby, employees and patrons watched as the twisters danced west and south of the Denny's Restaurant along I-40, restaurant manager Danielle Landers said.

"We had about seven tables at the time," she said. "There were a few people that wanted to go outside and see the tornadoes, but most people waited inside until the storm passed. We didn't see any damage."

Near Tulsa, a storm toppled trees and damaged at least one house, a mobile home and an auto dealership as it moved through around 1 p.m.

Resident Leslie Shanks said he saw a tornado twist a tree in his front yard and noticed that another tree had fallen onto the back of his house.

"It hit and was gone," Shanks told the Tulsa World.

Some 2,618 Oklahoma Gas & Electric customers and between 3,000 and 4,000 AEP-PSO customers lost electric power at the height of the storms. Service had been restored to all but 1,200 AEP-PSO customers by 8 p.m., officials said.

His conclusion will be debated throughout the week-long conference, as other researchers present opposing papers that say changing wind and temperature conditions in the tropics are due to natural events, not the accumulation of carbon dioxide emissions clouding the Earth.

Many of the experts gathered in the coastal city of Monterey, California, are federal employees. The Bush administration contends global warming is an unproven theory.

While many of the conference's 500 scientists seem to agree that a warming trend in the tropics is causing more and stronger hurricanes than usual, not all agree that global warming is to blame.

Some, like William Gray, a veteran hurricane researcher at Colorado State University in Fort Collins, Colorado, attributed the warming to natural cycles. Gray said he believes salinity buildups and movements with ocean currents cause warming and cooling cycles. He predicted the Caribbean water will continue to warm for another five to 10 years, then start cooling.

MORE WARMING TO COME

Whatever the cause, computer projections indicate the warming to date -- about one degree Fahrenheit (half a degree Celsius) in tropical water -- is "the tip of the iceberg" and the water will warm three to four times as much in the next century, said Thomas Knutson, explaining projections from the National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey.

Adam Lea, a postdoctoral student at Britain's University College London in Dorking, Surrey, presented research based on British, German, Russian and Canadian studies that concludes half of the increased hurricane activity in the tropics could be attributed to global warming.

Holland, director of the Mesoscale and Microscale Meteorology Division of the federal research center, said tropical storm anomalies in the 1940s and 1950s can be explained by natural variability.

But he said carbon dioxide started changing traceable patterns in the 1970s and by the early 1990s, the atmospheric results were affecting the storm numbers and intensities.

"What we're seeing right now in global climate temperature is a signature of climate change," said Holland, a native of Australia. "The large bulk of the scientific community say what we are seeing now is linked directly to greenhouse gases."

Hurricane Katrina, which tore onto the Louisiana and Mississippi coasts on August 29, was the deadliest Atlantic hurricane in 77 years and the costliest ever, with property damages estimated at $75 billion.

This year, the weather service's Tropical Prediction Center expects more hurricanes than usual, but not as many as last year's record 14.

The 1,745-meter (5,745-feet) San Cristobal volcano has been active for several years, but seismic activity, small eruptions and gas releases in the crater, have increased since Friday.

"In every period there is a phase of strong activity with high tremors" during which explosions can occur inside the crater, Ineter said.

Between 30,000 and 50,000 people live around the volcano. The last time a significant eruption phase occurred was November 1999, with moderate explosions coming from the crater.

Reefs are vital habitat for fish, lobsters and other sea life that feed and breed in the sheltered waters. The reefs also deflect storm waves that might otherwise wash away the beaches that are at the heart of the region's multibillion dollar tourism industry.

Bleached and infested with disease, coral off Puerto Rico and the Virgin Islands is in poor shape, scientists said in interviews last week. They said further bleaching wouldn't be apparent before summer and it would take some time after that before they would know if more coral died.

"You don't know how scary it looks down there," said Zandy Starr, who monitors coral and sea turtles in St. Croix's national parks. "All of us thought that by now, with all the cooler temperatures in January and February, we would have seen recovery, but they're still sick."

Glassy, calm seas have permitted coral-killing ultraviolet rays to penetrate to the ocean floor, warming water temperatures and making the fragile undersea life more susceptible to disease, Starr said.

A record 9 percent of elkhorn coral -- vital for reef building -- died last year and more was damaged, Rogers said. Growing some eight inches a year, elkhorn is one of the faster generating coral, while other coral grows just a half-inch or so each year.

Scientists haven't pinpointed what caused coral to become sick or led to the warm water, which stresses coral and makes it more susceptible to disease. They can't say whether global warming is a factor.

"We don't really have the data. You need a record over decades. There's a lot of research that needs to happen," said Alberto Sabat, a biology professor at the University of Puerto Rico.

But the trend of warmer waters isn't limited to the Caribbean. The National Oceanic and Atmosphere Administration said waters were warmer than usual in the South Pacific, mid-Atlantic and Indian Ocean in mid-April.

Rogers said coral fared far better after hurricanes that devastated the U.S. Virgin Islands in 1989 and 1995 because the storms cooled the sea, allowing reefs to recover more quickly from damage.

Rising temperatures appear to be "something new that the corals aren't used to," said Tyler Smith, a marine researcher at the University of the Virgin Islands.

The scientists worry that the problem is being overlooked.

"People just don't know that much about coral because it's underwater. If 40 percent of the trees in one of our national parks died, people would take notice," Rogers said.