Changing Snowcover, Temperature, and Streamflow Patterns in a Pacific Northwest Watershed

The Oregon Cascade range receives over 2500 mm of precipitation annually making it one of the wettest places in the US, despite a pattern of seasonal drought and summer low flows. Because snow in much of the Cascades accumulates close to the melting point, future warming would mean that large areas could shift from a snow- dominated to a rain-dominated winter precipitation regime (Nolin and Daly, 2006), with the potential for higher winter peak flows and lower summer low flows. In this work, we examine long-term records of snow depth, surface air temperature and streamflow at the H. J. Andrews Long Term Ecological Research (LTER) site. Situated in Lookout Creek watershed on the western side of the Oregon Cascades, this LTER is characterized by rugged topography. It spans a precipitation gradient from the snow-dominant zone, the rain-snow transition zone, to the rain-dominant zone. Analyses of snow depth, temperature, and streamflow show that the expected patterns of climate change are not straightforward. Other factors such as temperature inversions (controlled by atmospheric circulation) and geology affect snowmelt and streamflow dynamics.