Natural Resources, School of

 

School of Natural Resources: Dissertations, Theses, and Student Research

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First Advisor

Mark Svoboda

Second Advisor

Francisco Muñoz-Arriola

Committee Members

Tsegaye Tadesse

Date of this Version

5-2026

Document Type

Thesis

Citation

A thesis presented to the faculty of the Graduate College at the University of Nebraska in partial fulfillment of requirements for the degree of Master of Science

Major: Natural Resource Sciences

Under the supervision of Professors Mark Svoboda and Francisco Muñoz-Arriola

Lincoln, Nebraska, May 2026

Comments

Copyright 2026, Quinton R. Deppert. Used by permission

Abstract

In 2002, Dr. Mark Svoboda characterized a new form of drought known as flash drought. Flash drought was defined as a rapid decline in vegetation health caused by severe heat and drought. In recent years, attempts to quantify the impacts of flash drought via precipitation, soil moisture, evapotranspiration, and temperature indicators have proliferated. What has rarely been quantified is what the rapid decline in vegetation health amid flash drought looks like through remote sensing. This is because vegetation health indices like the Normalized Difference Vegetation Index (NDVI) are derived from the visible and infrared regions of the electromagnetic spectrum and rely on long observation windows to filter observations to those with the least cloud cover. Modern flash drought definitions characterize a rapid onset or intensification of drought conditions that occur over the course of weeks to at most a month and require indicators with daily or near-daily observation windows. Despite over four decades of investigation, NDVI remains best suited for medium to long-term drought monitoring, not flash drought monitoring. To observe vegetation health in a shorter observation window will require bypassing one of the fundamental limitations in optical remote sensing: cloud cover. Vegetation optical depth (VOD), a microwave-based proxy for vegetation water content and structure, is insensitive to cloud cover. Whether VOD can be used to monitor flash drought impacts on vegetation has yet to be demonstrated through rigorous validation across scales via optical satellite vegetation products and in situ biomass, which this study does for a limited spatial extent.

Advisors: Mark Svoboda and Francisco Muñoz-Arriola

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