Year of Award

2019

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Forestry

Department or School/College

W.A. Franke College of Forestry and Conservation

Committee Chair

Solomon Dobrowski

Commitee Members

Zack Holden, Andrew Larson

Keywords

drought, soil moisture, remote sensing, vegetation water content, vapor pressure deficit

Subject Categories

Environmental Monitoring

Abstract

Drought stress is a major contributing factor to adult tree mortality and limits regeneration across the globe. Drought effects are often studied on a site level, but recent advances in remote sensing allow for observations of plant water status across broader geographic scales. The vegetation optical depth (VOD) derived from satellite sensor microwave backscatter has been shown to be sensitive to canopy water content, and can therefore provide useful information on how plant water status changes over time. We develop an index which quantifies the normalized difference between diurnal VOD retrievals (nVOD) across the western U.S. to determine where plant water status is sensitive to variations in water supply (soil moisture) and atmospheric water demand (VPD). Diurnal variability in canopy water content (as expressed through nVOD) was most sensitive to soil moisture variation at intermediate water deficits and sites with low tree cover. These areas occur in ecotones between forest and grasslands or shrublands, and also occur at values of climatic water deficit (CWD) where nVOD is most sensitive to both soil moisture and VPD variation.

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© Copyright 2019 Drew S. Lyons