Quantifying the spatial temporal variability of annual streamflow and meteorological changes in eastern Ontario and southwestern Quebec using wavelet analysis and GIS

To make good policy decisions, knowledge of the trends and patterns in regional and local fluctuations in water resources and the influence of regional meteorological conditions are required. This study quantified the spatial–temporal variability of annual streamflow variations and meteorological changes in parts of eastern Canada. Time series and Geographic Information System (GIS) methods were used to evaluate the potential influence of low frequency climate change on annual spring flood onset and streamflow amplitude over a 24 year period. Continuous wavelet (CWT) and cross-wavelet transforms (XWT) were used to detect and extract temporal changes in the annual streamflow cycle amplitude, and to determine its relative phase shift to a standing 1-year sine wave through time. This was done to determine spatial–temporal differences and trends in the annual flood onset, and to determine the differences in the range between flood and background levels in 23 hydrological stations in eastern Canada. The study was carried out in the eastern Ontario/southwestern Quebec region of Canada because of the relatively high spatial density of hydrological stations from generally pristine waterways, as well as the high density of meteorological stations with uninterrupted recordings for a 24 year period from 1/1969 to 12/1992. This research indicates that over this 24 year period, the southwestern part of the region, along the US border, experienced an increase in temperature of up to 0.05 °C/year, and a decrease in precipitation of ∼0.5 mm/month; the predominantly rural northwest region warmed only <0.02 °C/year and became <0.2 mm/year wetter. During the same time interval, the annual streamflow shifted on average to a ∼20 days earlier flood onset, following the similar northwest–southeast trend of the meteorological records. In the northwest, along the Ottawa River, flooding occurred approximately 50 days earlier in the early 1990s than in the late 1960s, while it was less than 10 days earlier in the southeastern streams. The streamflows of the Ottawa and Rideau River, the main waterways that were studied, have generally lower annual streamflow amplitudes than the smaller and more pristine waterways that experience more seasonality, while the annual streamflow amplitude does not show any significant trend in time and space.