QUANTIFYING THE GLACIAL MELTWATER COMPONENT OF STREAMFLOW IN A NORTH CASCADE BASIN USING A DISTRIBUTED HYDROLOGY MODEL

The Middle Fork of the Nooksack River is important for municipal water supplies, power generation, and fish habitat. Summer discharge in the Middle Fork is in part sustained by meltwater from the Deming Glacier on Mount Baker, WA, which is a concern for water resource managers in the region because Deming Glacier is retreating. We used the Distributed Hydrology Soils Vegetation Model (DHSVM) to perform a detailed assessment of the hydrology in the Middle Fork basin. DHSVM is a physically based, spatially distributed hydrology model that simulates a water and energy balance at the pixel scale of a digital elevation model. DHSVM requires GIS input grids and meteorological data to characterize the watershed and simulate streamflow. Once calibrated, the model was applied to examine the influence of glacier size on streamflow and to simulate streamflow based on predicted future climate change scenarios.

The model was used to simulate streamflow using the current glacial coverage and three water years (2003 through 2005) of meteorological data from the basin. The late summer glacial meltwater contribution to streamflow from these simulations ranged from 8.4% for the wettest water year, to 26.1% for the driest water year. When the glacier size was reduced buy 17%, the late summer glacial meltwater contribution lowered to 5.5% and 19.2% for the wettest and driest water years, respectively. We also created hypothetical meteorological data inputs using predicted climate changes for the Pacific Northwest. When compared to current flow conditions, these simulation results indicate that a 15.7% reduction in late summer streamflow could occur when the glacier size is reduced by 17%, suggesting that fish habitat and the use of the Middle Fork Nooksack as a water supply source may be compromised in the future.