With a rainstorm on its way, three Kalahari zebras head for a favorite water source. Zebras can follow the Kalahari rains for more than 100 miles in search of fresh water and grazing. Rain here is an unpredictable phenomenon, usually in the form of violent thunderstorms with winds up to 60 miles per hour that easily destroy crops or human settlements. Monsoon winds off the Indian Ocean help bring rain in the Kalahari summer, but the rainy season starts at the end of the year and peaks in rainfall in January and February.
Rainy season comes and the Kalahari is transformed into a grassy savanna. As one 1950s observer commented, "this was no Sahara, but a ... picture ... of pleasant parkland." A good thing for elephants like these, walking proof that the Kalahari is not the desert it can sometimes seem. Instead, thanks to its variable rainfall and temperature, the Kalahari is technically a semi-desert. Travel north and the rainy season could start in November and last until May. Head south and the rains could start months later and die down much earlier. The Kalahari experiences some of southern Africa's greatest extremes of temperature: highs can soar to 120 degrees F; lows can fall well below freezing.
As the rainy season begins and temperatures soar upward, the desert comes to life. The abundance of water lets one of the Kalahari's most imposing residents, the African bullfrog, one of the world's largest frogs, emerge from his subterranean home. Before the dry season sets in and temperatures fall, he must find a mate and then play nursemaid to the tadpoles that result. As he works, he will have the sun on his back. In January, Kalahari temperatures can soar as high as 120 degrees F.
An impala, a South African antelope, makes its way through a flooded strip of Kalahari grassland in the high rainy season. Impalas, like the springbok and gemsbok antelope that also inhabit the Kalahari, graze on a variety of grass in wet times and scrounge for roots or nibble on wild melons in dry times. Herds of impala do not usually venture more than 5 miles from a permanent water supply. When the rains stop, this can prove tricky. Most water in the region is lost through evaporation or quickly soaked up by the Kalahari's sands. Nor is the importance of fresh water supplies lost on the Kalahari's human inhabitants. In Botswana, home to most of the desert, the name of the national currency, "pula," means "rain."
As the Kalahari's dry season comes to an end, powerful fires rage across its plains, fed by an abundance of brittle, straw-like grass. But these fires are not entirely destructive. Studies have found that the blazes act as accelerants for new vegetation -- the release of fresh nutrients into the air from burning organic material is thought to feed the Kalahari's soil. Subsequent grass grows more quickly and shrubs show denser growth. The fires can also prove a feasting bonanza for the Kalahari's wildlife, which scavenge its burned-out plains for dead insects, rodents, and snakes. NASA reports that some Kalahari fires are hot enough to feature cumulus clouds on top of their pillars of smoke.
Though part of the region's standard climate cycle, droughts are severe in the Kalahari. The desert's name, in Tswana (one of the tribal languages of Botswana, home to 80 percent of the Kalahari) is Kgalagadi, or "The Great Thirst." The Kalahari has almost no surface water, a situation that made it the last region of Africa surveyed by European explorers. The landscape shown here could go months or even a year without water. During the dry season, low relative humidity and temperatures up to 109 degrees Fahrenheit mean any moisture does not last for long. It's either soaked up by the Kalahari's sands or quickly evaporated.
As the rainy season draws to a close, this flock of flamingoes and their new, gray babies, prepare to leave the Makgadikgadi pans for their coastal homes. The Kalahari's salt pans, flat basins that constitute the dried-out remnants of ancient rivers and lakes, provide the primary source of surface water for wildlife during the rainy season. Flamingo flocks fly for hundreds of miles to reach the Makgadikgadi pans in northern Botswana to nest and hatch their chicks. At 4,600 square miles, the pans, believed to be the world's largest, are thought to be the flamingoes' ancient home. But the dry season in the Kalahari does not necessarily mean a warm season and these birds require sunnier climes. Temperatures in the Kalahari can fall as low as 37 degrees F by July with frost dotting its savannas.
Surging into the stony Kalahari basin, the Okavango River brings with it visions of green. The river is the life source of the Okavango Delta, a patchwork of channels and islands that contain one of southern Africa's richest collections of vegetation, and is believed to have fathered the ancient Lake Makgadikgadi, perhaps the world's largest salt pan. The delta's flood plains vary in size with rainfall -- from 2,300 to more than 5,020 square miles -- but this area remains steadfastly green, providing sustenance to elephants and crocodiles alike.
With the start of the dry season, wildebeest travel with zebra across the Kalahari in search of water and food. Though the wildebeest can receive moisture from the grass, leaves, and plants they consume, without water they are unable to digest this fodder. And with the onset of drought, even these resources will be denied to them. Instead, using their infallible scent for water, they head for far-off rivers and lakes. Generally, wildebeest migrate in the early morning, evening or night when the sun is at its lowest and the Kalahari's temperatures may be hovering above freezing. These treks consume much of the animals' energy, making them prime targets for attacks from lions, leopards or hyenas.
Part mud, part water, this one-time savanna makes for tricky travel. Equipped with a thinner fur for the desert's elevated temperatures, Kalahari lions are specially equipped to handle their home's harsh climate. They can go for months without water -- a fact that allows them to survive the area's often lengthy dry season. Feasting on mice, badgers, rabbits, foxes, and whatever other wildlife they can kill provides them with moisture. During the dry months, a lion pride will break up, the females heading off with their babies, the males left to fend for themselves. Despite the protection, however, cub mortality rates in the Kalahari are much higher than in more temperate zones.