URI grad student evaluates sediments in Pettaquamscutt River estuary
Todd McLeish, 401-874-7892
1,000-year record of southern New England precipitation suggests increasing variability in future rainfall
NARRAGANSETT, R.I. -- October 5, 2005 -- Future precipitation rates in southern New England will likely remain similar to those in recent decades, but increasing variability may mean that dry years will be drier and wet years will be wetter. That is the conclusion drawn by University of Rhode Island graduate student J. Bradford Hubeny, who sampled sediments in the Pettaquamscutt River estuary to determine “moisture budgets” for the last millennium.
The Pettaquamscutt River estuary has a deep section that lacks oxygen and where the sediment doesn’t get stirred up, resulting in annual sediment layers like tree rings that indicate precipitation rates. It’s the only estuary or bay in the Northeast with the right conditions to create these annual sediment layers over long periods of time.
“In the years when there was a lot of rain, run-off from the surrounding land deposited more material into the water that eventually sank to the bottom,” explained Hubeny, who is studying geological oceanography at URI’s Graduate School of Oceanography. “The more rain in the region, the thicker the layer of sediment that formed.”
Originally from Hingham, Mass. and now living in Cranston, Hubeny took eight core samples 1-2 meters deep and counted and analyzed the sediment layers to determine precipitation rates as far back as the year 1024.
During the first part of the Little Ice Age (1500 to1700), when local temperatures were 1-3 degrees cooler than today, southern New England had about 30 percent less precipitation in an average year than in modern times. During that period, rainfall amounts were also much less variable from year to year than today.
During the 500 years before the Little Ice Age, precipitation rates were similar to those in the last 300 years, but there was slightly more variability than in more modern times. Based on this precipitation record, Hubeny believes that the region may be entering a period of increasing variability in precipitation rates.
“Periodic fluctuations in rainfall amounts should come in two- to nine-year cycles, and in the low years precipitation could be similar to those in the Little Ice Age,” Hubeny said. “I think we have a generally good outlook for the future, but there could be some tough years, especially if we get into a nine-year cycle that could bring us four straight years of drought.”
According to Hubeny, predicting future weather patterns is tricky, especially given the uncertainty of the effect of global warming on precipitation. One global warming scenario suggests that if temperatures continue to rise in coming decades, precipitation in southern New England will continue to be relatively high and variable. However, another potential scenario suggests that increasing temperatures will lead back to Little Ice Age conditions and a decline in precipitation rates over a long period of time, which could lead to future water shortages.
Hubeny will report the results of his research at the annual meeting of the Geological Society of America Oct. 16 to19 in Salt Lake City.