Orange River Basin Freshwater in Average Year

The majority of the runoff occurs in the Lesotho highlands and below the Orange Vaal confluence runoff is erratic. On the whole runoff is low in the Orange basin. Rainfall decreases westward within the basin meaning the rainfed headwaters are the main source of the river’s volume. Only during the period Dec to Feb is there a slight change with some areas of the South West corner of the basin showing slightly higher runoff. This is consistent with the location of the Lesotho highlands. The period May to September experiences the least rainfall in the headwater region, resulting in dry conditions during these months.

Freshwater Legend (mm/month)

Bargraph referencing the colours on the evaporation maps.

Other Orange Maps

Orange Freshwater Maps