It is one of the dark mysteries of colonial America: the disappearance of 120 settlers at North Carolina's Roanoke Island in the late 16th century. Only a tree carving was left behind.

At Jamestown two decades later, others tried their hand at colonizing the New World. Thousands died during the "starving time" as settlers ate boiled shoe leather, dogs and even their own dead.Scientists analyzing centuries-old cypress trees now believe the settlers arrived during the region's worst drought in the past 800 years, bringing starvation and death to both English-speaking settlements.

The evidence does not clear up what happened at Roanoke Island, but it helps explain some of the hardships, said Dennis Blanton, an archaeologist at the College of William and Mary and co-author of a study published this week in the journal Science.

"The English could not have found a worse time to found their settlements in the New World," he said. "There were other factors, but the drought clearly contributed to their major problems."

Jamestown, the first permanent English settlement in America, was founded in 1607 in the midst of the driest seven-year period in 770 years. Only 38 of the 104 original settlers survived the first year; 4,800 of 6,000 people who lived there died between 1607 and 1625.

"It challenges your imagination to try and understand how it could have been so horrendous," Blanton said.

The new knowledge, he said, challenges the notion that the Jamestown settlers were ill-prepared because they were greedy.

"They were profit-motivated, but this drought would have challenged any group of people," Blanton said. "If it weren't for bad luck these guys wouldn't have had any luck at all."

Blanton teamed with tree-ring specialists from the University of Arkansas, to research the effect weather may have had on the settlements.

One of the Arkansas researchers, Matthew Therrell, said his group gathered hints of weather conditions by measuring the width of tree rings from the trunk of the bald cypress, which can live for 1,000 years or more.

They found that the rings were much smaller than average during the years of the Roanoke Island settlement, 1587 to 1589, and in 1606 to 1612, the early years at Jamestown. The two areas are 100 miles apart.

"Our estimate for drought during that period is that there was a very severe one," Therrell said.

No precise weather data are available from the colonies, but the tree-ring data from that era are similar to a short-term drought recorded in tree rings from the 1940s in the same area. According to Virginia climate records, the area received only about half the normal rainfall in 1941. The drought that hit the colonists lasted much longer and thus was more severe.

The years 1587 to 1589 marked the most extreme drought of any comparable period during the 800 years of the tree-ring record.

It was during this time that the people of Roanoke, including Virginia Dare, the first English child born in America, disappeared. The settlement became known as the "Lost Colony."

A ship that left them in America went back to England for supplies and returned in 1590 to find the colony abandoned. The only trace was a tree carving of the word "Croatoan," the name of a nearby Indian tribe.

What happened at Jamestown is easier to follow. The settlers came from England planning to buy their food from Indians.

"They were dismayed to have the Indians tell them that they didn't have enough corn to go around," Blanton said. "The drought information suggests that the Indians were telling the truth."

Settlers wouldn't have been familiar with the local climate, Blanton said. The area looked lush, and the level of the nearby James River would have been unaffected because it is a tidal river.

The drought made fresh, good-quality groundwater scarce, leaving the colonists thirsty and suffering from associated illnesses.

Conflict erupted when the Indians could not supply food as promised. The settlers couldn't leave the confines of their fort to fish or hunt for fear of attack by the Indians.

When the supplies they brought from England ran out or spoiled, the settlers ate boiled shoe leather, tree bark, dogs and rats, said Diane Stallings, the National Park Service historian at the Jamestown site.

A few even turned to cannibalism. One settler killed his pregnant wife, threw the fetus into the river, cut up his wife's body and ate the parts, Stallings said, citing a written account from the period. The man was executed for his acts.