Low-frequency variability in Southwestern Canadian stream flow: Links with large-scale climate anomalies

By applying a suit of statistical techniques, this study investigated the impacts of the El Nino-Southem Oscillation (ENSO), the Pacific-North America (PNA) pattern, the West Pacific (WP) pattern and the Pacific decadal oscillation (PDO) teleconnections on the interannual to interdecadal variability of southwestern (SW) Canadian streamflow anomalies. It is shown that El Nino (La Nina) episodes lead to significant negative (positive) streamflow anomalies in several subregions during the spring and/or summer months following the ENSO onset year. A simple composite analysis of streamflow for anomalous PNA years conditioned on non-ENSO years showed that the high phase of PNA could also produce an El Nino-like streamflow response over the region. In addition, the ENSO-streamflow relationship appears to be modulated by the interdecadal oscillation of the North Pacific (NP) climate as indexed by the PDO. The interaction between PDO and ENSO was found to be constructive when the two are in phase and destructive otherwise. The potential of using the three large-scale climate anomalies (ENSO, PNA and PDO) for long-range streamflow forecasting in SW Canada was assessed using a partial correlation analysis with the southern oscillation index (SOI), the PNA and PDO indices at lead times of up to 10 months. While partial correlations with all three indices were found to be statistically significant for several basins, the ENSO and PDO effects appear to be far more important than that of the PNA pattern. The winter season SOI, which is an indicator of the mature phase of ENSO, shows modest correlations with basins whose flow regimes are dominated by winter rain/spring snowmelt. On the other hand, the winter season PDO shows relatively strong correlations with basins originating in the Rocky Mountains, whose flow regimes are dominated by spring-summer snow/glacier melt. The modest SOI-streamflow relationships are partly attributed to nonlinearity induced by the interference from the extratropical sources of variability (i.e. PNA and PDO). Long-range streamflow forecasting strategies for this region should thus incorporate information from the three large-scale climate anomalies. Copyright (C) 2006 Royal Meteorological Society.