AGU Abstract Submitted: Secular Streamflow Trends in Watersheds Receiving Mixed Rain and Snow, Pacific Coast and Cascades Ranges

The following abstract was submitted for the Fall AGU meeting:

Secular Streamflow Trends in Watersheds Receiving Mixed Rain and Snow, Pacific Coast and Cascades Ranges

A. Jefferson, University of North Carolina at Charlotte

Much existing research has focused on detecting climate change effects on snowmelt-dominated watersheds, but in the Pacific Coast and Cascades ranges, precipitation falls as either rain or snow, depending on latitude, elevation, and season. Watersheds often straddle the snow line, with some areas dominantly receiving rain and higher elevations accumulating seasonal snowpacks. These snowpacks are near the 0°C threshold, making them sensitive to the effects of climate warming. Climate sensitivity of seasonal and event hydrographs from watersheds with mixed rain and snow has not been fully explored. This project investigates detectable climate change signals in long-term streamflow records in the Washington, Oregon, and northern California Coast and Cascades Ranges.

Watersheds with mean elevations above the seasonal snow line show significant increases in streamflow during January through March and decreases in the percent of annual flow during April through June, the historical snowmelt period. These changes were not detectable in watersheds with mean elevations below the seasonal snow line. There were no consistent trends in peakflow dates or volumes. The multiple drivers of peakflow occurrence make it unlikely that any changes in peakflow timing will be detectable for several decades. Results suggest that Coast Range hydrology has been minimally impacted by historical climate warming, but that Cascades Range watersheds are already experiencing altered hydrologic regimes.

Pending acceptance, the work will be presented in session H32 Spatial and Temporal Trends in Hydrometeorological Records as Indicators of Climate Variability and Change.

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