Modeling the Effects of Forecasted Climate Change and Glacier Recession on Late Summer Streamflow in the Upper Nooksack River Basin

Abstract

Like many watersheds in the North Cascades range of Washington State, USA, streamflow in the Nooksack River is strongly influenced by precipitation and snowmelt in the spring and glacial ice melt in the warmer summer months. With a maritime climate and high relief containing approximately 34km2 of glacial ice, the streamflow response in the Nooksack River basin is sensitive to increases in temperature. Climate projections from global climate models (GCMs) for the 21st Century indicate increases in temperature with variable changes to precipitation. The watershed is a valuable freshwater resource for regional municipalities, industry, and agriculture, and provides critical habitat for endangered salmon species. Thus, understanding the impacts of forecasted climate change is critical for water resources planning purposes. I apply publically available statistically derived 1/16 degree gridded surface climate data along with the Distributed Hydrology Soil Vegetation Model (DHSVM) with newly developed coupled dynamic glacier model to simulate hydrologic and glacial processes through the end of the 21st Century. Simulation results project median winter streamflows to more than double by 2075 due to more precipitation falling as rain rather than snow, and median summer flows to decrease by more than half with a general shift in peak snowmelt derived spring flows toward earlier in the spring. Glaciers are projected to retreat significantly with smaller glaciers disappearing entirely. Ice melt contribution to streamflow is likely to play an important role in sustaining summer baseflows in the Nooksack River. Glacier melt derived streamflow is projected to increase throughout the first half of the 21st century and decrease in the latter half after glacier ice volume decreases substantially