POTENTIAL INFLUENCE OF CLIMATE ON FLOOD RECURRENCE IN THE WINOOSKI RIVER WATERSHED, VERMONT

Predictions for future climate changes in the Northeastern United States are for higher precipitation but more drought periods. This translates to fewer, but more intense storm events which should increase the likelihood of flood events. In this study, we use long-term USGS stream gauges to evaluate if this trend has been occurring over the last 80 years. The Winooski River watershed is located in northern Vermont, flowing through Montpelier and discharging into Lake Champlain. Three gauging station exist in the Watershed, two on the main trunk stream and one on a tributary (North Branch). The area drained by the North Branch is rural and population in the area is relatively unchanged for many decades. The remaining two stations are on the main trunk stream in Montpelier and near the discharge point in suburban Burlington. The North Branch provides an opportunity to evaluate changing precipitation patterns that might influence surface hydrology with minimal anthropogenic influence. The watershed has an area of 2600 km² while the North Branch has an area of only 179 km². Peak annual discharge values for the North Branch range from 14.8 to 45.9 m³ s^-1. Excluding two outliers, the peak discharge drops to 31.7 m³ s^-1. When looking at daily average discharge values for the entire record, only 81 of the top 100 days have occurred in the last 25 years. Interestingly, 18 of the remaining 19 days were in the mid-1930’s. An analysis of the top 500 daily average discharges further supports this with a significant majority occurring since 1982. A graph of peak annual discharge versus year shows an increasing trend with time that is significant at 95% confidence. An evaluation of 10-year events by decade also shows an increasing trend with an r² of 0.84 that is significant at 95% confidence. Similar analyses for the gauging stations at Montpelier and Essex Junction do not show similar trends. This might suggest that watershed management in the more populated areas has overshadowed a possible climate signature for stream discharge.