Detection and attribution of variability and trends in streamflow records from the Canadian Prairie Provinces

Emerging period of record trends and low frequency (i.e. centennial-scale) variability were examined in streamflow records over the entire Canadian Prairie Provinces. The average record length was 52 years, with the longest record spanning 1911-2010. A modified Mann-Kendall trend analysis showed decreasing flows in Alberta and in southwestern Saskatchewan, no significant trends in the central Prairies and increased flows in Manitoba. Using composite analysis, this study also detected the impacts of the Pacific Decadal Oscillation (PDO), the North Pacific Index (NPI), the El Nino-Southern Oscillation (ENSO) and the Pacific North American mode (PNA) on mean daily discharge. There are increased flows during the negative phases of the PDO and PNA, La Nina events and weak Aleutian lows, and decreased flows during the positive phases of the PDO, El Nino and strong Aleutian lows. A much weaker effect of the Arctic Oscillation (AO) was detected. The similar to 60-year cycle of the PDO has important implications for the recognition of emerging trends in streamflow in response to global climate change. Separation of an emerging consistent trend from the confounding transient trend from PDO phase was greatly facilitated by streamflow time series that span at least one and a half PDO cycles.