LONG-TERM TRENDS IN STREAM DISCHARGE IN THE NORTHEAST UNITED STATES: EVIDENCE FOR CHANGING CLIMATE

Predictions for future climate changes in the northeastern United States are for higher total precipitation but more drought like periods. This translates to fewer, but more intense storm events which may increase the likelihood of flood events. In this study, we use long-term USGS stream gauges and NWS land stations to evaluate if this trend has been occurring. Streams in the northeast U.S. with a minimum of 50 years or more of data in rural locations with little apparent recent change in land use were selected for analysis. This provides an opportunity to evaluate changing precipitation patterns its influence on surface hydrology with minimal anthropogenic influence. There were a total of 33 stream gauging stations from Maine, New Hampshire, Vermont, Delaware, Maryland, New Jersey, Pennsylvania, Massachusetts, Connecticut, and New York examined. In each location annual peak discharge, annual daily mean discharge, days with more than 0.5 in of precipitation, annual total precipitation, and annual peak precipitation were tested statistically against time using linear regression analysis at 95% confidence. Throughout the northeast there is a general increase in all five of these parameters. Twenty-eight of the locations showed an increase in annual peak discharge (75% are significant), 29 with increasing annual daily mean discharge (90% are significant), 28 with increasing days with more than 0.5 in of precipitation (82% are significant), 25 have increasing trends in total annual precipitation (88% are significant), and 23 locations show increasing trends in annual peak precipitation (78% are significant). Many of the discharge and precipitation time series show an apparent cyclicity. This suggests the influence of both climate change and longer-term atmospheric oscillations in the study locations. The apparent increase in precipitation and subsequently discharge indicate an increased risk for future flooding in the northeast U.S.