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College

College of Science and Engineering

Major

Environmental Science

Faculty Mentor

Se-Yeun Lee

Faculty Editor

Lyn Gualtieri

Student Editor

Ivonne Lares and Jean Simpson

Abstract

The City of Seattle depends on the Tolt River for both drinking water and hydropower. Hydrologic models have been employed to assess the future effects of climate change on streamflow in the area, which ultimately impact hydropower generation and the drinking water supply. However, the main issue with these models is that they assume vegetation growth and change to be static, overlooking the potential impact on streamflow. The objective of this study is to investigate the effects of vegetation change on streamflow in the Tolt River by analyzing climate and streamflow data and vegetation indexes. The study examines the impact of climate variability, particularly the Pacific Decadal Oscillation (PDO), on streamflow. Additionally, the study calculates changes in forest area within the watershed, identifies the year of occurrence, and determines the change in streamflow due to changes in vegetation. The findings show that summer streamflow in the North Fork subbasin decreased after a forest area decreasing event, while decreases in summer streamflow in the South Fork subbasin were due to climate change.

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