Spatiotemporal Variability in Distributions of Western Streamflow Conditioned on Climate Indices

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San Francisco, CA

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We investigated spatial and temporal variations in the mean and distributions of annual streamflows in the Western US conditioned on indices for ENSO, PDO, and AMO and their interactions for water years 1912 through 2010. Distribution properties were quantified using the 10%, 25%, 50%, 75% and 90% quantiles. Although others have examined the spatiotemporal variations in anomalies of precipitation means for the Western US that were conditioned on indices for ENSO, PDO, and AMO, no parallel studies have been conducted for streamflow. Spatial and temporal patterns in negative and positive anomalies of the mean in annual flows conditioned on individual climate indices for AMO, PDO, and Darwin sea level pressure (SLP), our ENSO indicator, differed from the annual streamflow anomalies of the quantiles examined. North-south bipolar differences in streamflow anomalies for low Darwin SLP occurred in the 90th quantile of annual flow anomalies, but were not evident in the anomalies of the mean. No distinct bipolar effects of PDO were apparent in our results. AMO had limited effect on anomalies of the mean in annual streamflow in the West. But in the southern half of the west (S-W) and along the Rocky Mountains, large positive anomalies occurred in quantiles above the median during cool AMO and large negative anomalies occurred during warm AMO. Effects of interactions between PDO and ENSO were constructive or destructive. So depending on the PDO phase, effects may have appeared opposite of the expected for ENSO. Since effects of AMO were largest in the S-W and along the Rockies, warm AMO in combination with PDO and ENSO resulted in large areas of the West with negative flow anomalies in quantiles above the median. The greatest area in the Western US affected by drier and intensely dry conditions occurred during positive AMO, negative PDO, and positive Darwin SLP, similar to current climate conditions and those of the 1950's. Our results reveal differences between mean streamflows and streamflow distributions as quantified by quantiles in the Western US. These differences add to and transform our understanding of effects of climate conditions on the full distribution of streamflows. Enhanced understanding of streamflow variability associated with climate interactions has direct applications in improving water supply forecasting and managing water and related resources.


Abstract H33O-05 presented at 2012 Fall Meeting, AGU

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