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This study demonstrates how the regional climate affects river flow in the upper Limpopo Valley of southern Africa (21-24.5S, 26-30E). The catchment basin receives inflow from the Crocodile, Marico, Mahalapse and Lotsane Rivers, and lies on the eastern fringe of the Kalahari plateau, known for water-deficit conditions. Different ways to represent the surface water balance are compared. The annual cycle of gains from precipitation (P) spikes upward in late summer (Jan-Mar), while losses from evaporation have a broad peak in early summer (Oct-Dec). Different formulations of the surface water balance yield a range of values from -0.21 to -1.69 mm/day, depending on how evaporation is quantified. An analysis of global climatic influences on the Limpopo River found that high flow coincides with Pacific La Nina, low pressure over the central Atlantic and local upper easterly winds that draw tropical moisture from the Mozambique Channel. There is little trend in Limpopo River flow during the study period 1959-2014; however, CMIP5 model projections exhibit a downtrend in the surface water balance. A new insight is that evaporation losses are well represented by sensible heat flux in semi-arid environments.