The coherent of African river flows: Composite climate structure and the Atlantic circulation

Abstract

The composite structure of the ocean and atmosphere around Africa is studied in the context of river flow variability. Annual streamflows are analysed for the Blue and White Nile, Congo, Niger, Senegal, Zambezi, and Orange Rivers, and inflow to Lake Malawi. Spectral energy is concentrated in 6.6-and 2.4-year bands. The interannual variability of many river flows is significantly cross-correlated (p < .05) over the period 1950-1995, following removal of the mean trend. A combined river flow index indicates that flows were highest in 1961, 1962, 1968, 1977, 1978 and lowest in 1971, 1972, 1982, 1983, 1991. Forming a composite of differences between high-and low-flow years, SST anomalies and other atmospheric fields are investigated to better understand climatic factors driving hydrological extremes. During high flows, NCEP reanalysis data reveal a composite La Nina event off Peru-Ecuador. SST patterns reveal an inter-hemispheric dipole in the Atlantic (eg. warm - north) and below normal SST in the west Indian Ocean during years with high flow.

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