ACKNOWLEDGEMENTS Glacier Melt Makes a Significant Contribution to Summertime Upper Hood River Streamflow This work is supported by the USGS, the Mazamas, the Anne Nolin and Jeff Phillippe Association of American Geographers, and the Department of Geosciences, Oregon State University Geological Society of America

Introduction Results

Mount Hood is the tallest mountain in Streamflow Location Percent from Glaciers Oregon and its 6 of its 11 glaciers feed Eliot Creek 87.7% into the five irrigation districts in Hood River Valley. Mount Hood’s glaciers Coe Creek 88.0% have receded up to 61% in the past Upper Middle Fork Hood River 74% century and are projected to continue decreasing with further climate warming. Nearly of the August streamflow in the Upper Middle Fork Hood River is derived from the Eliot and Coe glaciers. Because glaciers store precipitation as snow and ice during winter and release it via meltwater during summer, glacier meltwater reduces the interseasonal How Might Summertime Flows Change as the and interannual variability of streamflow. However, the volume of meltwater Our approach uses a combination of direct streamflow measurements and a from Mount Hood glaciers is not known because the glacial-fed streams are not degree-day glacier melt hydrologic model. Glaciers Become Smaller? gaged. The focus of this work is on current and projected glacier meltwater contributions to streamflow from three glaciers that feed two main branches of We use the Snowmelt Runoff Model (SRM) with melt factors and the Hood River. runoff coefficients adjusted for the glaciers and calibrated using our The specific objectives are to: discharge measurements. 1. Determine the interseasonal and interannual proportions of glacier coniferous forest Using recent rates of glacier meltwater to streamflow in the Middle Fork Hood River and West Fork recession (Lillquist and Walker, Hood River; 2006; Keith Jackson, personal 2. Estimate changes in glacier meltwater production on timescales of 10- to communication) we estimate 50-years and impacts on peak flows and low flows in the Middle Fork that the areas of Eliot and Coe Hood River and West Fork Hood River. glaciers will decrease by approximately 50% by 2057. Using this new glacier area in Do Glaciers Really Influence Basin-Scale Discharge? SRM, we find that the glacier -derived flow is reduced by Six water height recorders were installed: 50.5%. two at the termini of Eliot and Coe glaciers, Fraser Alpine ISA Fraser Fool Creek ISA four at locations lower down. Data from This means that the flow at the the water height recorders were calibrated Eliot Creek and Coe Creek using in situ flow measurements. irrigation diversions will be Streamflow fluctuations are driven by reduced by 44%. Flows further changes in air temperature. downstream below the confluence of Eliot and Coe Creeks will be reduced by approximately 37%. Conclusions Glacier melt is an important contributor to streamflow in the Upper Oxygen isotope samples were collected to Middle Fork Hood River at the points where the irrigation districts divert discriminate from streamflow derived from glacier water. With continued glacier recession, flows will show significant melt and from grounwater. When considering the entire Hood However, for the Upper Middle Fork decreases. River Basin, Mount Hood’s glaciers Hood River, when you consider the Samples were collected directly from glacier ice, comprise less than 1% of the area. point at which the irrigation districts from meltwater at the glacier terminus, at springs, Lillquist K., and K. Walker, Historical Glacier and Climate Fluctuations divert streamflow, the glaciers and at locations downstream.. A 2-component at Mount Hood, Oregon, Arctic, Antarctic, and Alpine Research, 38(3), comprise nearly 8% of the area. mixing model was used to estimate contributions 399-412, 2006. from glacial and non-glacial sources.