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Date Permissions Signed

2-23-2018

Date of Award

Winter 2018

Document Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

Mitchell, Robert J. (Geologist)

Second Advisor

Clark, Douglas H., 1961-

Third Advisor

Yearsley, John R.

Abstract

Stream temperatures in mountain streams in the western Cascade Mountains are heavily influenced by factors such as discharge, air temperature, and as in the case of the Nooksack River Basin in northwest Washington State; snow and glacial melt. The Nooksack basin is sensitive to warming climates due to the regions moderate Pacific maritime climate. Previous modeling studies in the upper Nooksack basins indicate a reduction in snowpack and spring runoff, and a recession of glaciers into the 21st century due to global climate change. How stream temperatures will respond to these changes is unknown. We use the Distributed Hydrology Soil Vegetation Model (DHSVM) coupled with a glacier dynamics model to simulate hydrology and the River Basin Model (RBM) to model stream temperature from present to the year 2090 in the North, Middle, and South forks of the Nooksack River basin.

We simulate forecasted climate change effects on hydrology and stream temperature using gridded daily statically downscaled data from 10 global climate models (GCMs) of the Coupled Model Intercomparison Project Phase Five (CMIP5) with two different representative concentration pathways (RCP) RCP4.5 and RCP8.5. Simulation results project a trending increase in stream temperature into the 21st century in all three forks of the Nooksack. There is a strong correlation between rising stream temperatures and warming air temperatures, decreasing stream discharge; and snow and glacial meltwater. We find that the highest stream temperatures and the greatest monthly mean 7-day average of the daily maximum stream temperature (7-DADMax) values are predicted in the lower relief, unglaciated South Fork basin. For the 30 years surrounding the 2075 time period, the mouth of the South Fork is forecasted to have a mean of 115 days above the 16 °C 7-day average of the daily maximum stream temperature threshold. Streams in the Middle and North fork basins with higher elevations that sustain more snow and glacier ice are slower to respond to warming climates due to meltwater contributions, especially in the next 50 years. Towards the end of this century, when snowpack and glacial volume is greatly decreased, the buffering effect of meltwater declines, and the North and Middle forks experience larger increases in mean daily stream temperature. For the 30 years surrounding the 2075 time period, the mouths of the Middle and North forks are forecasted to have means of 35 and 23 days, respectively, above the 16 °C 7-DADMax threshold.

Type

Text

Publisher

Western Washington University

OCLC Number

1027788284

Digital Format

application/pdf

Geographic Coverage

Nooksack River Watershed (Wash.)--Environmental conditions

Genre/Form

masters theses

Language

English

Rights

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

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Geology Commons

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