American Meteorological SocietyPotomac River Streamflow Since 1730 as Reconstructed by Tree Rings

Abstract

A 248-year reconstruction of the low-flow (July, August and September) period of the Potomac River indicates that the prolonged drought of the 1960s may have been the most severe since 1730. However, there appear to have been several long periods of about 50 years in length when flow was generally above or below the long-term median flow. The period from 1900 through 1950, which comprises most of the measured flow period, was generally above median. Long-period climatic shifts can have important water resource implications. The Potomac River streamflow at Point of Rocks, Maryland was reconstructed by using tree-ring chronologies from sites in or near the river basin. Canonical regression analysis was used to reconstruct simultaneously July, August and September discharge after screening all the tree-ring predictors. Verification statistics and cross-spectral analysis indicate that the average reconstruction of these three months is most reliable for periods longer than about six years and shorter than about three years. Spectral analysis of the reconstruction indicates the presence of a 15.7-year periodicity that warrants verification through examination of meteorological data, as well as through additional streamflow reconstructions in the region.