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Date of Award

Summer 2025

Document Type

Masters Thesis

Department or Program Affiliation

Environmental Studies

Degree Name

Master of Arts (MA)

Department

Environmental Studies

First Advisor

Berardi, Gigi M.

Second Advisor

Laso, Francisco

Third Advisor

Konrad, Christopher P. (Christopher Peter)

Abstract

In Washington’s Water Resource Inventory Area 1 (WRIA 1), a potentially decades-long legal process to clarify legal water use, called the Nooksack Adjudication, began in 2024. About 70% of water used in WRIA 1 is for agricultural irrigation, yet accurate, field-level estimates of irrigation withdrawals remain unavailable. Agricultural water meter data are sparse, inconsistent, self-reported, and difficult to validate or link to specific water rights. Previous studies in WRIA 1 have focused on basin-wide water budgets or theoretical crop demand estimates and lacked the spatial resolution or reliability needed to provide evidence for adjudication proceedings. To address this gap in data, I developed four models based on satellite-derived evapotranspiration and precipitation data to estimate monthly water withdrawals for irrigation at the field scale across WRIA 1 from 2011 to 2023. All models were optimized and validated using the best available water meter data as ground truth controls. The highest-performing model, SWBR-13, uses a soil water balance approach with 13 tunable parameters to account for effective precipitation and stored water. The SWBR-13 model demonstrates strong performance, with area-normalized irrigation depth errors symmetrically distributed around zero (mean = 1.35 mm, median = 0.17 mm) and moderate overall accuracy (mean absolute error = 19.8 mm; median absolute deviation = 21.66 mm). The expected percentage error for a single prediction is 62%. While this level of uncertainty limits its use as a definitive accounting method, the model provides a transparent, scalable approach for estimating irrigation in WRIA 1. These results mark a critical step toward filling longstanding irrigation data gaps in the region. They can help farmers document their water use, support policymakers in evaluating claims under adjudication, and inform regional water management and planning efforts.

Type

Text

Keywords

Adjudication, agriculture, evapotranspiration, Geographic Information Systems (GIS), hydrology, irrigation, modeling, Nooksack River Basin, remote sensing, water balance, water rights, WRIA 1

Publisher

Western Washington University

OCLC Number

1531273457

Subject – LCSH

Water rights--Washington (State)--Nooksack River Watershed; Irrigation water--Washington (State)--Nooksack River Watershed--Measurement; Evapotranspiration--Washington (State)--Nooksack River Watershed--Remote sensing; Agriculture--Washington (State)--Nooksack River Watershed--Water-supply; Water use--Washington (State)--Nooksack River Watershed--Measurement--Statistical methods; Watershed management--Washington (State)--Nooksack River Watershed; Irrigation farming--Washington (State)--Nooksack River Watershed; Irrigation--Washington (State)--Nooksack River Watershed--Computer simulation; Hydrologic models--Washington (State)--Nooksack River Watershed

Geographic Coverage

Nooksack River Watershed (Wash.)

Format

application/pdf

Genre/Form

masters theses

Language

English

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Rights Statement

http://rightsstatements.org/vocab/InC-NC/1.0/

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

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