Year of Award

2025

Document Type

Thesis

Degree Type

Master of Science (MS)

Degree Name

Geosciences

Other Degree Name/Area of Focus

Hydrogeology

Department or School/College

Geosciences

Committee Chair

Dr. W. Payton Gardner

Committee Co-chair

Dr. Andrew C. Wilcox

Commitee Members

Dr. W. Payton Gardner, Dr. Andrew C. Wilcox, Dr. Douglas J. Brinkerhoff

Keywords

groundwater, Climate, recharge, mountain

Subject Categories

Geology | Hydrology | Other Earth Sciences

Abstract

Changes to groundwater recharge and stream flow were simulated from downscaled CMIP6 global climate models in a headwater catchment of the Blackfoot River, MT. A calibrated, 3-D, coupled surface and groundwater GSFLOW model, forced with minimum and maximum temperature, and precipitation from a downscaled CMIP6 simulation was used to quantify groundwater recharge and stream flow. The model was calibrated against measured groundwater head and stream flow using observed temperature and precipitation boundary conditions. The calibrated model was then forced with downscaled temperature and precipitation from the CANESM5 model for the SSP245, 370 and 585 scenarios, as well as a manual increase to temperature only using historical climate. Groundwater recharge was quantified as the flow out of the soil zone into the saprolite or lower bedrock layer, as simulated by the MODFLOW UZF package. Results indicated that despite lower snowfall fractions and a loss of recharge efficiency, the predicted increase in precipitation resulted in an overall increase in groundwater recharge and stream flow in the watersheds. Differences in geology resulted in the lower bedrock K (Cap Wallace) watershed receiving a more stochastic increase in recharge a month earlier than the higher bedrock K (North Fork) watershed. While the magnitude of average annual recharge was similar between watersheds, the Cap Wallace watershed was predicted to have greater increases in baseflow, while the North Fork watershed maintained slightly increased late season flow due to enhanced bedrock groundwater storage. Simulations which only increased temperature resulted in reduced groundwater recharge regardless of underlying geology. These results had important implications for predicting changes to groundwater recharge under climate change, as the covariant changes in precipitation and temperature could directly affect groundwater recharge and stream flow generation.

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