Linking observed and general circulation model upper air circulation patterns to current and future snow runoff for the Rocky Mountains

Snowmelt runoff from alpine areas is the primary source of streamflow and w ater supply in western North America. Increasingly, questions about the imp acts of global climate change on watershed yield are being asked. This pape r is a forecast of expected changes to runoff for two key rivers in western North America. The paper develops and applies linkages between historical and general circulation model (GCM) upper air circulation patterns deemed t o control winter precipitation in the northern Rocky Mountain states and so uthern Alberta. Historical and 1 x CO2 GCM upper airflow conditions are qui te similar, but there are substantive variations in the GCM 2 x CO2 upper a irflows. Relative occurrence (dominance) of historical synoptic patterns is statistically linked to historical spring runoff for the Oldman and Colora do Rivers. These linkages are used to forecast variation in the future runo ff on the basis of variations in synoptic pattern statistics for the 2 x CO 2 GCM upper airflow patterns.