Publication Date

5-2023

Date of Final Oral Examination (Defense)

11-14-2022

Type of Culminating Activity

Dissertation

Degree Title

Doctor of Philosophy in Geoscience

Department

Geosciences

Major Advisor

James P. McNamara, Ph.D.

Advisor

Hans-Peter Marshall, Ph.D.

Advisor

Alejandro Flores, Ph.D.

Advisor

Nancy Glenn, Ph.D.

Abstract

Knowledge of the complex interaction between snow, vegetation, and streamflow in semiarid mountain climates is necessary for predicting water resources. The effects of warming temperatures on snow distribution will cascade into vegetation water use and streamflow. Due to our reliance on snow water resources, it is necessary to understand how vegetation affects snow distribution, how vegetation uses snow water inputs and the subsequent effects on streamflow in the current and warming climate. The overall objective of this research is to improve our understanding of snow-vegetation interactions in a semiarid climate. In this dissertation, I use field data to evaluate how vegetation impacts snow accumulation and melt, and how snow distribution and climate parameters affect vegetation. I then apply a physically based model to understand how warming temperatures across the rain-snow transition will affect snow water input for vegetation water use. In the first chapter, I introduce the primary objectives and provide background for the following chapters. In the second chapter, I use field data at two different locations to evaluate how vegetation affects the snow surface energy and mass balance. I found forests accumulate less snow, have a lower cold content to overcome before melting starts and shade the snow surface slowing the melt rate. In the third chapter I estimate evapotranspiration (ET) at five sites spanning the rain-snow transition and I compare ET to climate parameters. Annual ET at the low elevation site is controlled by a balance between spring precipitation and supplying water and energy drivers. The site in the rain-snow transition follows the soil moisture availability, increasing annual ET with precipitation. Annual ET at the middle and high elevation sites increases with an earlier snow disappearance date. In the fourth chapter, I apply a physically based model to evaluate how warming temperatures alter the rain-snow transition and subsequent ET and streamflow. I found warming temperatures in the fall reduce peak SWE, increase fall streamflow, and shift spring streamflow earlier but have limited effects on ET. Warming temperatures in the spring increase ET and shift spring streamflow timing earlier. Increasing ET rates in the spring lead to reduced ET rates in the summer. Additionally, the forest and seasonal snow zones are most sensitive to warming temperatures. This dissertation advances our understanding of how snow and vegetation interact and how vegetation will respond in a warming climate.

DOI

https://doi.org/10.18122/td.2043.boisestate

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