Glacier retreat is an extensively studied effect of climate change, and the Pacific Northwest is a hot spot for climate change–induced glacier retreat, with 858 glaciers contained in an area of 466 square kilometers. Runoff from shrinking glaciers can both increase and decrease summertime streamflow in alpine regions, but climate change also affects snow accumulation, evapotranspiration, and other hydrological factors that influence streamflow.
Few studies have examined how all of these factors might interact to alter future streamflow as climate change progresses. New research by Frans et al. predicts differing timelines for the effects of melting glaciers on streamflow at high versus low elevations in the Pacific Northwest.
The authors investigate this interplay using a high-resolution computer model to predict glacier and streamflow dynamics between 1960 and 2099 for six river basins fed by glaciers in the Pacific Northwest. The model incorporates regional climate data and is calibrated with real-world observations of glacier size and streamflow.
The six selected river basins span a range of elevations and climates, allowing for comparison between settings—from a high-precipitation setting with low-elevation glaciers in the Olympic mountain range, for example, to a drier, continental climate in the Cascades. The researchers’ analysis of the model projections shows that glacier retreat in all six basins will accelerate throughout the 21st century. However, the resulting effects on streamflow are projected to vary according to elevation.
At higher elevations, the model projects, glaciers will remain big enough for their meltwater to buffer large declines in seasonal snowfall until late in the century. At that point, high-elevation glaciers will have shrunk too much for continued melting to support historic summertime streamflow levels. However, lower-elevation glaciers are already small enough that they will stop enhancing streamflow as soon as 2020 in some regions.
These new findings could help clarify the potential effects of glacier retreat on water resources and ecology in the Pacific Northwest. The authors note that continued advancements in computing and in remote sensing techniques to measure glacier size will enhance future efforts to model the streamflow effects of shrinking glaciers. (Water Resources Research, https://doi.org/10.1029/2017WR021764, 2018)
—Sarah Stanley, Freelance Writer