Climate of the Orange-Senqu River Basin

Within the geographically extremely heterogenic Orange-Senqu River basin there are enormous climatic differences. The climate in the basin is usually discussed in terms of these regions

• The mountainous terrain of the Maloti Mountains of Lesotho - this region experiences a relatively temperate climate, defining the ecosystems and to a large extent the livelihoods possible in this region.
• The undulating dry grasslands of the southern Highveld - a climatic and geographic transition zone from the mountainous regions.
• The western region of southern Africa - containing three desert systems, characterized by harsh arid conditions:
  • The Succulent Karoo – experiencing highly variable and inconsistent rainfall throughout the year
  • The Nama Karoo - receiving mainly summer rainfall and comprising a number of different vegetation types
  • The Southern Kalahari – consisting of deep wind-blown sand, which allows little or no run-off from rainfall

(UNDP-GEF 2008)

The map below illustrates the distribution of these terrestrial ecoregions across the Orange-Senqu River basin.

Terrestrial Ecoregions of the Orange-Senqu River basin.

Source:WWF 2001

( click to enlarge )

The altitude and mountains of the Lesotho Highlands ensure a temperate climate. Source:Lesotho Water Commission 2009 ( click to enlarge )

The arid Nama Karoo. Source:DRFN 2004 ( click to enlarge )

The physical factors that create distinct climatic zones and the variability within these zones are discussed in the following sections.