Assessing the Hydrologic Impacts of Disturbance-Altered Canopy Structures in the Mountain West
Authors
Manning, Aidan
Issue Date
2023
Type
Dissertation
Language
Keywords
Critical Zone Hydrology , Forest Disturbance , Forest Managment , Snow Hydrology , Watershed Management
Alternative Title
Abstract
Large, high severity forest disturbances are altering the hydrology of snowmelt-supplied water resources across the aridifying Western US, challenging our capacity to anticipate and adapt to changes in water supply and demand. The naturally complex structure of forest canopies drives variation in water and energy fluxes at fine scales. Combined with variety in climate and terrain, heterogeneity in existing forest structure and among individual disturbance scenarios drives uncertainty in the effects of disturbance on snowpacks and streamflow. This dissertation aims to better understand and constrain this uncertainty by exploring the effects of varied disturbances and canopy impacts on snowpack and streamflow across scales and sites. We use ground-based long-term observations of streamflow and climate in Southern Colorado to estimate streamflow response to an understudied insect outbreak disturbance at a headwater basin scale. We find mixed responses of no change to large increases in streamflow after disturbance in six affected basins. We then leverage tree ring records and high-resolution snowpack observations to explore the effects of canopy structure on snow-forest interactions at fine scales in the Northern Sierra Nevada, finding predictable patterns of snow depth and tree moisture sensitivity across small gaps in forest canopy. Finally, we combine high-resolution observations and process modeling with machine learning at operational scales to identify key predictors of snowpack response to disturbance that are transferable between sites and disturbance scenarios, highlighting the roles of initial forest conditions and variables that drive snowpack sublimation.