Temporal variability modes of floods for catchments in the St. Lawrence watershed (Quebec, Canada)

We analyzed the temporal variability modes of annual maximum flow of 15 pristine tributaries of the St. Lawrence River in Quebec during the 1934-2000 period in relation to six climatic indices, using principal component analysis, linear regression, the Mann-Kendall test, correlation analysis and canonical correlation analysis. As for temporal variability modes, we identified three variability modes: two on the south shore (on both sides of 47 degrees N) and one on the north shore. A statistically significant temporal trend (positive trend) was observed in the flood time series of the north shore mode only. This increase appears to be due to the continental nature of the climate, which features a strong contrast between the rainy decades (positive anomaly) and the dry ones (negative anomaly). The former (the 1970s and 1980s) followed the latter (the 1940s, 1950s, and 1960s). However, the three modes were characterized by two synchronous anomaly periods on a decadal scale: a negative anomaly during the 1950s and a positive anomaly during the 1970s. That said, these two synchronous periods were characterized by greater amplitude on the north shore than on the south shore. Thus, the dry (wet) periods were dryer (wetter) on the north shore than on the south shore. As for the relationship between the climatic indices and streamflow, Atlantic Multidecadal Oscillation (AMO) was correlated to the north shore mode. ENSO (El Nino/Southern Oscillation Index) was correlated to the south shore mode located north of 47 degrees N) and AO (Arctic Oscillation) was correlated to the south shore mode located south of this parallel. This study shows that floods are not influenced by the same climatic indices on both shores of the St. Lawrence River in Quebec. (C) 2010 Elsevier B.V. All rights reserved.