A wavelet approach to the short-term to pluri-decennal variability of streamflow in the Mississippi river basin from 1934 to 1998

The temporal variability of streamflow in the Mississippi river basin, including its major tributaries (Missouri, Upper Mississippi, Ohio and Arkansas rivers), was analysed using continuous wavelet methods in order to detect possible changes over the past 60 years. Long-to short-term fluctuations were investigated. The results were compared with SOI, PDO and NAO indices and precipitation time series and were also processed by wavelet methods. A major change point around 1970, also reported in other works, was recovered in all climate and hydrological processes. It is characterised by the occurrence of an 8-16-year mode for Upper Mississippi and Missouri and of a 3-6-year mode for all rivers. Two other discontinuities around the mid-1950s and 1985 were also detected. A strong power attenuation of the annual cycle in the Arkansas, Upper Mississippi and Missouri rivers was also found between 1955 and 1975. In general, the dominant modes of inter-annual to pluri-annual streamflow variability lay in the 2-4-year, 4-8-year and 10-16-year ranges, which was typical of SOI for the period of study. A preferential link with the Mississippi basin headwater zone (i.e. Upper Mississippi and Missouri) was deduced during the approximate to 1934-1950 and approximate to 1970-1985 periods. Overall, the contribution of inter-annual to pluri-annual oscillations ranged from 6.6 to 26% of streamflow variance, while the short-term scales (<2-3 weeks) explained from 1.1 to 6.4%. The annual cyclicity explained from 19.1 to 48.6% of streamflow variance. High-frequency streamflow fluctuations linked to synoptic activity were also found to increase after 1955 for all basins except Upper and Lower Mississippi, apparently modulated by a approximate to 2-4-yr oscillation. Copyright (C) 2010 Royal Meteorological Society