Climate influences on Vaal River flow

Abstract

A study of climatic influences on Vaal River discharge, near Johannesburg, South Africa, finds that peak summer flows in the period 1979–2014 coincide with ocean–atmosphere interaction in the east Atlantic. The analysis has three parts: inter-annual influences by correlation of summer discharge with climate fields, atmosphere and ocean composites of 14 peak flow months, and a case study flood in January 2010 and its regional scale forcing. Inter-annual links are established with low pressure over the east Atlantic and an eastward equatorial ocean current and suppressed upwelling in the northern Benguela. During the January 2010 flood in the Vaal River, flow increased to 2 801 m³/s. There was a low salinity plume and warm sea temperatures off Angola > 29°C. A terrestrial vegetation fraction > 0.6 and corresponding latent heat fluxes enriched NW-cloud bands over the Vaal River catchment, during the flood case study of January 2010. Comparison of (Pacific) Southern Oscillation and east Atlantic influence on Vaal River discharge reveals the former drives evaporative losses while the latter provides an advance warning of flow variability.