Paleo-reconstruction of summer streamflow with estimates of uncertainties and applications to climate change assessments

Long-term paleo proxy reconstructions of streamflow help characterize climate variability and extreme climatic events, such as droughts, which play a crucial role in water resource planning. We use the Variable Infiltration Capacity (VIC) hydrological model to produce estimates of warm season (April-September) streamflow and streamflow uncertainty, based on observed relationships between cool season precipitation and warm season streamflow. The Upper Yakima basin WA is used as a test case for the methods. Over 300 years of basin-average cool season precipitation were dendrochronologically reconstructed using multiple linear regression and principle components analysis. Temporally and spatially distributed cool season precipitation patterns, resampled from the historic record so as to span the reconstructed range of natural variability, were then used to construct an ensemble of historic warm season flow associated with each reconstructed year from the paleological record. This procedure quantifies the inherent uncertainty in summer flow estimated for each year. The ensemble of extended meteorological data was then perturbed using a composite delta method (averaging the temperature and precipitation changes from several climate models) and used to drive the VIC hydrologic model to examine the potential impacts of climate-change on summer flow over the 300-year long reconstructed flow record.