A PALEO-PERSPECTIVE ON FUTURE DROUGHT CONDITIONS IN SOUTHERN NEW ENGLAND

Regional drought concerns associated with global warming call for a better understanding of the climate system through high-resolution paleoclimate archives. To this end, we have produced a varve thickness time-series from the Pettaquamscutt River Estuary, Rhode Island in order to examine moisture budgets in Southern New England over the last millennium. Each couplet consists of an organic-rich spring layer overlying a predominantly clastic lamination. The clastic lamination thicknesses are significantly correlated to average annual precipitation totals for the State of Rhode Island from 1895 – 2001 AD (r = 0.469, p < 0.0001). This correlation is due to increased runoff from the watershed during times of higher rain, and subsequent increases in the rate of clastic input to the water column and sediment surface. Using the regression between precipitation and clastic lamination thickness, we have calibrated our data to form a time-series of Southern New England precipitation. During the Little Ice Age (LIA; ca. 1500 – 1700 AD), there was significantly less precipitation (ca. 73% of modern values) in Southern New England (ANOVA: F = 96.36, p << 0.0001). This change is most likely due to a southerly shift of the Jet Stream, which made cold, dry arctic air the dominant air mass over Southern New England. During the Medieval Warm Period and modern times, precipitation values were higher (means of 92.2 cm and 95.3 cm, respectively, versus 69.1 cm for LIA) and more variable (standard deviations of 29.5 and 33.4, respectively, versus 18.1 for LIA). Our data suggest that if temperatures continue to rise in the upcoming decades, precipitation in Southern New England will continue to be relatively high. In this scenario, precipitation should exhibit periodic fluctuations of 2-9 years with maximum droughts of ca. 77% of average modern values during 1-4 year stretches. If, on the other hand, anthropogenic forcing causes thermohaline circulation to become reduced (ie. Little Ice Age conditions), Southern New England may expect average precipitation values to be reduced by ca. 27% over potentially long periods of time, which would cause serious water shortage issues in the future.