The Kalahari is a vast expanse of southern Africa covering approximately 900,000 square kilometers across Botswana, Namibia, and South Africa. Often mistakenly classified as a barren desert, it is actually a semi-arid sandy savanna that supports extensive grasslands and woodlands. Unlike the hyper-arid Sahara, the Kalahari receives between 250 and 500 millimeters of rainfall annually, sufficient to sustain a remarkable diversity of life. This region is defined by its dramatic annual cycle of transformation, dictated by the presence or absence of water.
The Long Dry Season (May to October)
The period from May to October marks the long dry season, which includes the region’s coldest winter months. The landscape takes on a pale, dormant appearance as vegetation conserves moisture. While days are often warm, reaching up to 26°C, the lack of cloud cover causes night temperatures to plummet frequently to near or below freezing, especially in June and July.
Surface water vanishes almost entirely, forcing wildlife to concentrate around remaining waterholes and man-made boreholes. Animals like the gemsbok and springbok are adapted to this scarcity, relying on moisture obtained from roots, tubers, and tsamma melons buried beneath the sand. Large herbivores must manage their nutrient intake carefully, as the tough, dry grasses require them to consume greater volumes for sustenance.
As the dry season progresses into September and October, temperatures begin to rise significantly before the rains arrive. Daytime highs can soar past 34°C, creating a period of intense heat and low humidity that challenges all forms of life. This escalating heat serves as a transitional phase, making the arrival of the first summer rains a welcome event for the parched landscape.
The Local Wet Season and Summer Growth (November to April)
The local wet season, corresponding to the Southern Hemisphere summer from November to April, radically changes the Kalahari environment. Moisture often arrives suddenly in the form of intense afternoon thunderstorms, though the timing remains unpredictable. This local rainfall is the primary source of water for the savanna, initiating a rapid transformation known as the “green flush.”
Within days of the first substantial downpours, the dry earth bursts into life with new shoots of grass and a proliferation of ephemeral plants and wildflowers. This abundance of fresh, nutritious grazing allows herbivores to disperse away from centralized water sources and spread across the savanna. The renewed resources stimulate major breeding cycles, including the synchronized calving of antelopes and the emergence of meerkat pups.
The wettest months, typically January and February, feature high heat and humidity, contrasting sharply with the cold dryness of the preceding winter. Migratory birds return to take advantage of the insect boom and plentiful seeds, adding to the seasonal biodiversity. This period of plenty sustains the ecosystem until the rains taper off around April, leading back into the dry cycle.
The Critical Role of the Okavango Flood Pulse
The annual Okavango Flood Pulse is unique to the northwestern Kalahari, operating on a timing independent of local rainfall. The water feeding the Okavango Delta originates from heavy summer rains that fall months earlier in the Angolan highlands, over 1,000 kilometers away. This external water source begins its slow journey through the river system, seeping into the Delta’s vast network of channels and floodplains.
The paradoxical nature of the flood is that the water arrives in Botswana, peaking typically between June and August, precisely when the local area is experiencing its driest and coldest winter months. Because the region is flat, the floodwaters creep forward at an extremely slow pace, sometimes only a kilometer per day. This delayed, gradual inundation creates a massive, counter-seasonal oasis in the dry savanna.
This influx of water sustains an immense concentration of wildlife during the most challenging time of the year for the rest of the Kalahari. The Delta’s seasonal expansion, which can swell its size from 6,000 to over 15,000 square kilometers, provides a lifeline of fresh grazing and permanent water. This feature ensures wildlife populations have a refuge to survive the dry season.