[1] Using wavelets, statistically significant interannual and interdecadal oscillations that occurred haphazardly have been detected in southwestern (SW) Canadian seasonal precipitation anomalies. At interannual scales, station precipitation anomalies show unstable relations with large-scale climate anomalies such as the El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Pacific/North America (PNA), East Pacific (EP) and West Pacific (WP) patterns, and the Central North Pacific (CNP) index. Not all significant precipitation activities could be matched by similar activities in one or more climate anomalies considered. Inconsistent wavelet coherence and phase difference between the leading principal components (PC) of regional precipitation anomalies and climate indices as well as weak Pearson's correlations between bandpassed precipitation PCs and climate indices for the 2-3 year and 3-8 year scales provide supporting evidence for unstable precipitation climate relationships at the interannual scale. On the other hand, interdecadal precipitation variability is mainly associated with low-frequency variability in CNP, PDO and ENSO. Composite analysis of winter precipitation shows that ENSO, PDO, PNA and WP offer better separation of positive and negative precipitation anomalies than EP and CNP. However, the effect of ENSO is found to be stronger than the others. Precipitation power spectrum plots mostly reveal two linear decay regions of different slopes separated by a breakpoint located approximately at 20 to 30 days, while empirical probability plots reveal power law behavior and hyperbolic intermittency in these data, whose correlation dimensions (D 2 ) are between 8 and 9. Different multifractal behaviors are observed among stations because the amount of different rainfall generating mechanisms vary from station to station, as reflected by the haphazard nature of oscillations detected in most precipitation data. Although the leading PCs of winter regional precipitation show modest correlations at zero-to three-season lead times with ENSO and PDO indices, the high D 2 values and absence of consistent interannual precipitation activities suggest that prediction of SW Canadian seasonal precipitation by teleconnection with climate indices is likely limited. Adding other predictor fields such as sea surface temperature and/or sea level pressure may be useful.

By applying a suit of statistical techniques, this study investigated the impacts of the El Nino-Southern 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.

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[1] Changes to the North American snowpacks for 1979-2007 were detected from snow water equivalent (SWE) retrieved empirically from horizontally polarized brightness temperature (T B ) of a scanning multichannel microwave radiometer (18 and 37 GHz) and special sensor microwave imager (19 and 37 GHz) passive microwave data using the nonparametric Kendall's test. The predominant SWE trends detected agree with negative anomalies in snow cover observed in Northern Hemisphere since the 1980s, and both the SWE and snow cover results should be related to the significant increase in the surface temperature of North America (NA) observed since the 1970s. About 30% of detected decreasing trends of SWE for 1979-2007 are statistically significant, which is three times more than the significant increasing trends of SWE detected in NA. Significant decreasing SWE trends are more extensive in Canada than in the United States. The mean trend magnitudes detected for December-April are À0.4 to À0.5 mm/yr, which means an overall reduction of snow depth of about 5-8 cm in 29 years (assuming a snowpack density between 200 and 250 kg/m 3 ), which can impact regions relying on spring snowmelt for water supply. From detected increasing (decreasing) trends of gridded temperature (precipitation) based on the North American Regional Reanalysis data set and the University of Delaware data set for NA, their respective correlations with SWE data and other findings, such as global scale decline of snow cover, longer rainfall seasons, etc., it seems the extensive decreasing trends in SWE detected mainly in Canada are more caused by increasing temperatures than by decreasing precipitation. However, climate anomalies could also contribute to the detected trends, such as PC1 of NA's SWE, which is found to be correlated to the Pacific Decadal Oscillation index and marginally correlated to the Pacific North American pattern.

The impacts of large-scale modes of climate variability on the annual cycle of terrestrial hydrometeorology in the Canadian Columbia River basin were assessed with the aim of updating our current understanding and identifying opportunities for climate-informed, early-season water supply forecasting. Composite analyses of streamflow from seven Water Survey of Canada gauging stations conditional on El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Pacific/North American pattern (PNA), Arctic Oscillation (AO), and North Pacific Gyre Oscillation (NPGO) states revealed that hydrological impacts of a climate mode could be manifested through changes in the annual runoff volume and/or changes in seasonal runoff patterns. Responses were generally non-linear. Considering ENSO and the PDO, for instance, streamflow anomalies associated with their warm phases contrast with those associated with their cool phases; however, the warm phases tend to produce more consistent streamflow responses than the cool phases. More profoundly, the PNA and AO streamflow responses appear to be highly asymmetrical-only one phase (positive PNA and negative AO) is shown to significantly affect streamflow. Some North Pacific climate indices and ENSO show reasonably consistent and strong correlations with streamflow, which suggests that further refinement of climate-informed early season water supply forecasting is possible. It is shown that further improvement of forecast skills can be attained if North Pacific climate information is included in addition to ENSO in the current generation of operational statistical water supply forecast models.