PORTLAND – Snowfall in New England has decreased significantly in favor of rain during the last half of the 20th century, according to a study by the U.S. Geological Survey.

The study, published in the American Meteorological Society’s Journal of Climate, offers further evidence of a warming trend that could spell trouble for businesses that cater to skiers and snowmobilers.

“We compared the annual snowfall to total precipitation at 21 sites throughout New England and found a persistent trend from 1949 to 2000 of significantly less snow for 11 of those sites,” said Thomas Huntington, a USGS hydrologist in Augusta and the study’s lead author.

The remaining 10 sites had insignificant trends.

The strongest and most consistent trends were found at the four northernmost sites – Presque Isle, Ripogenus Dam and Millinocket in Maine, and First Connecticut Lake, N.H. They show an average decrease in annual snow-to-precipitation ratio from 30 percent in 1949 to 23 percent in 2000, Huntington said.

The percent of precipitation that fell as snow also generally decreased along the coast, with five of eight sites showing significant changes over the 50-year period.

Research also revealed significant correlations between snow-to-precipitation ratios in northern New England, air temperature, timing of spring runoff and atmospheric circulation.

The study included data from locations in Maine, New Hampshire, Vermont, Rhode Island and eastern Massachusetts. Sites in Connecticut and western Massachusetts lacked sufficient data to meet the study’s criteria, Huntington said.

He acknowledged that the trend toward less snow could signal a shortening of the ski season and the likelihood of an abbreviated stretch of spring skiing.

“We’re likely to see an earlier snow melt and more rain on snow,” he said.

Sunday River ski resort in Newry, which averages 155 inches of snow per year, has detected no trend in its snow totals, spokeswoman Susan DuPlessis said. “We’ve had some great snow years and some not so great snow years,” she said.

In any event, the industry’s growing reliance on man-made snow has lessened its dependence on the real stuff.

“Nowadays, the importance of natural snowfall is less than it used to be,” said David Rowan, publisher of Ski Area Management magazine in Woodbury, Conn. “Everyone makes snow. The temperatures are more critical than actual precip numbers.”

Huntington said the results of his study came as no surprise. “This is about the fourth or so in a series of studies which are all pointing in the same direction,” he said.

Previously published studies of late winter and early spring hydrologic changes in New England during the past century showed a one- to two-week advance in the halfway point of the winter-spring runoff and large increases in February river flows coupled with decreases in May flows, suggesting earlier snowmelt.

Earlier last-frost dates, lilac bloom dates and lake and river ice-out dates, along with data on thinning of river ice and spring air temperatures, also suggest that New England winters have lost some of their bite.

“Although these findings provide further evidence of a regional warming pattern, questions of the impact and cause of this trend are beyond the scope of this study,” said Huntington, “and this research does not identify whether the warmer climate in New England is linked to global climate change.”