Publication Date

8-2017

Date of Final Oral Examination (Defense)

5-2-2017

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Hydrologic Sciences

Department

Geosciences

Supervisory Committee Chair

Alejandro N. Flores, Ph.D.

Supervisory Committee Member

Jodi Brandt, Ph.D.

Supervisory Committee Member

Bangshuai Han, Ph.D.

Supervisory Committee Member

Rebecca L. Som Costellano, Ph.D.

Abstract

Seasonally snow-dominated, mountainous watersheds supply water to many human populations globally. However, the timing and magnitude of water delivery from these watersheds has already and will continue to change as climate is altered. Associated changes in watershed vegetation cover further affect the runoff responses of watersheds, from altering evapotranspiration rates to changing surface energy fluxes, and there exists a need to incorporate land cover change in hydrologic modeling studies. However, few land cover projections exist at the scale needed for watershed studies, and current models may be unable to simulate key interactions that occur between land cover and hydrologic processes.

To help address this gap in the literature, we explored the impacts of climate and land cover change on hydrologic regimes in the Upper Boise River Basin, Idaho. Using a multiagent simulation framework, Envision, we built a hydrologic model, calibrated it to historic streamflow and snowpack observations, and ran it to year 2100 under six diverse climate scenarios. Under present land cover conditions, average annual discharge increased by midcentury (2040-2069) with 13% more runoff than historical (1950-2009) across all climate scenarios, with ranges from 6-24% of increase. Runoff timing was altered, with center of timing of streamflow occurring 4-17 days earlier by midcentury. Our modeled snowpack was more sensitive to warming at lower elevations, and maximum snow water equivalent decreased and occurred 13-44 days earlier by midcentury. Utilizing metrics applicable to local water managers, we see the date that junior water rights holders begin to be curtailed up to 14 days earlier across all models by the end of the century, with one model showing this could occur over a month earlier. These results suggest that current methods of water rights accounting and management may need to be revised moving into the future.

To test the sensitivity of our hydrologic model to changes in land cover, we selected a projected future land cover from the FORE-SCE (FOREcasting SCEnarios of land-use change) model. Our future land cover produced less evapotranspiration and more runoff, which stemmed from misclassification of high elevation regions between the FORE-SCE model and our initial land cover dataset, due to changes in the NLCD (National Land Cover Database) classification methodology. Additionally, FORE-SCE does not explicitly model wildfire or vegetative response to climate, both of which will likely be major drivers of landscape change in the mountainous, forested, western U.S., potentially making it insufficient for land cover projections in these areas. With evapotranspiration being the only parameter changing between land cover types in our hydrologic model, we were unable to capture the totality of hydrologic response to land cover change and other models may be better suited for such studies. This study highlights the necessity for better land cover projections in natural ecosystems that are attuned to both natural (e.g., climate, disturbance) and anthropogenic (e.g. management, invasive species) drivers of change, as well as better feedback in hydrologic models between the land surface and hydrological processes.

DOI

https://doi.org/10.18122/B2ZX3R

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