Date of Award:

5-2016

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Civil and Environmental Engineering

Committee Chair(s)

Christopher M. U. Neale

Committee

Christopher M. U. Neale

Committee

Gilberto E. Urroz

Committee

Robert W. Hill

Committee

Joanna Endter-Wada

Committee

Jagath J. Kaluarachchi

Abstract

Theoretical water use of well-watered vegetation in the western United States was investigated by comparing a gridded dataset developed from satellite and ground instruments to weather stations representative of irrigated agricultural conditions. Since wetter environments are cooler and therefore subject to lower levels of evaporation than the same scenario with warmer temperatures, models derived from dryland and often populated areas overestimate potential plant needs in semi-arid or arid conditions. Evaluation of the model revealed an acceptable fit for air temperatures and solar radiation but with less confidence in humidity and wind speeds. Ultimately, the last two parameters were minor components in the calculation of reference evapotranspiration, which performed acceptably well at an hourly time step except for some high biases in states along the southern U.S. border. These findings substantiate application of the model for calculation of plant water requirements 1979-present in most areas.

Actual water use of invasive saltcedar was studied along the Colorado River in a wildlife refuge south of Palo Verde, California. Surface meteorological towers and groundwater wells measured water fluxes from 2006 until a fire burned the refuge and most of the equipment in August 2011. New instruments were installed and measured the evapotranspiration of the regrowth. Change in evapotranspiration was evidenced and models verified by a zeroed state. This control state of no (or nearly no) vegetation was very beneficial in this study. Saltcedar water use was assessed against other studies and the theoretical estimates mentioned above and found to be comparable to levels required by native vegetation.

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