Date of Award
2025
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Geology
First Advisor
Andrew W. Schroth
Second Advisor
E C. Adair
Abstract
Over the past century, winter temperatures and 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. Given that these events occur during winter when there tends to be less watershed monitoring and field activity, much remains to be understood regarding new water generation mechanisms in montane watersheds found in the northeastern U.S. Over three successive winters, we analyzed the combinations of soil (e.g. moisture and temperature), meteorological (rain amount and intensity, relative humidity), and snowpack (depth, snow water equivalent (SWE), cold content) conditions that enhance or diminish new water response during winter thaw events. In order to constrain this response, we leveraged a spatially distributed high-frequency sensor network and downstream USGS gage stream water sampling across a range of flow conditions in the Ranch Brook watershed, Stowe, VT. 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 20 mid-winter melt events. The fraction of new water ranged from 8% to 43%, with higher contributions during the winters of 2023 and 2024, which were characterized by frequent accumulation-ablation cycles, compared to 2025, when sustained subfreezing temperatures maintained a relatively cold snowpack. Intense rains and large changes in soil moisture were ubiquitous drivers of high new water across winters. Conversely, the role of snowpack conditions diverged depending on winter conditions with shallow snow depth, low SWE, and low cold content generating high new water under hydrologically dynamic winters, whereas under a sustained cold winter high SWE and high cold content conditions resulted in higher new water. During the three-year period, 7 of the 11 highest recorded discharge events occurred (4 summer storms, 2 freshets, and 1 ROS event), highlighting flashier responses in the hydrograph and soil moisture during snow-free periods. Our concomitant analysis of soil, snow, meteorological and hydrologic properties provides unique insight that is needed to quantify, manage, and mitigate increasingly common disturbances due to frequent winter weather whiplash.
Language
en
Number of Pages
84 p.
Recommended Citation
Williams, Garnet, "Integrating terrestrial, snowpack, and meteorological drivers of runoff generation during winter thaws in a montane catchment of the Northeastern U.S." (2025). Graduate College Dissertations and Theses. 2154.
https://scholarworks.uvm.edu/graddis/2154