Wavelet analyis of the interannual variability in southern Québec streamflow

Abstract

The objectives of this study are to describe the local interannual variability in southern Québec, Canada, streamflow, based on wavelet analysis, and to identify plausible climatic teleconnections that could explain these local variations. Scale-averaged wavelet power spectra are used to simultaneously assess the interannual and spatial variability in 18 contiguous annual streamflow time series. The span of available observations, 1938-2000, allows depicting the variance for periods up to about 12 yr. The most striking feature, in the 2-3-yr band and in the 3-6-yr band-the 6-12-yr band is dominated by white noise and is not considered further-is a net distinction between the timing of the interannual variability in local western and eastern streamflows, which may be linked to the local climatology. This opens up the opportunity to construct two regional time series using principal component (PC) analysis. Then, for each band, linear relationships are sought between the regional streamflow and five selected climatic indices: the Pacific-North America (PNA), the North Atlantic Oscillation (NAO), the Northern Hemisphere annular mode (NAM), the Baffin Island-West Atlantic (BWA) and the sea surface temperature anomalies over the Niño-3 region (ENSO3). The correlation analysis revealed the presence of a change point in the streamflow time series, as reported by others, occurring around 1970. For example, the west and east 2-3-yr bands are positively correlated to PNA since 1970, which was not the case prior to that change point. The proposed regional east-west divide is particularly evident prior to 1970, with a negative NAM correlation for the west and a positive NAM (and negative ENSO3) for the east. The picture for the less energetic 3-6-yr band is mixed, with alternating dominance of teleconnection patterns, but the 1970 change point holds.