Authors: Garnet Williams – University of Vermont
Title: Integrating terrestrial, snowpack, and meteorological drivers of runoff generation during winter thaws in a montane catchment of the Northeastern U.S.
Presentation Type: Poster
Abstract: Over the past century, winter temperatures and the proportion of precipitation falling as rain relative to snow have increased in the northeastern U.S. Winter warming has led to more frequent and intense mid-winter thaw and rain-on-snow (ROS) events that often trigger extreme hydrologic response. Over three successive winters, we analyzed the combinations of soil, meteorological, and snowpack conditions that enhance or diminish runoff response during winter thaw events. In order to constrain this response, we leveraged a spatially distributed high-frequency sensor network of soil, stream, meteorological stations, and outlet stream water sampling across the range of flow conditions in the Ranch Brook Watershed. New water contributions to event discharge were quantified at the watershed scale using 18O in a two-component isotope hydrograph separation over the course of 21 mid-winter melt events including the spring freshets. The fraction of new water during water year 2024 ranged from 13 to 45% for ROS events and 13 to 29% for thermal melt events. Water year 2023 generated a lower fraction of new water with a range of 9 to 26% for ROS and 22% for the only thermal melt event captured. Interannual and event-specific variability in new water contribution was influenced by several factors, including rain intensity, snowpack cold content, and snow depth. Events characterized by shallow snowpacks, low cold content, and high rain intensity tended to generate the highest new water.