The Okavango Delta, a vast inland wetland system, stands as a unique natural phenomenon within Botswana’s arid Kalahari Desert. Unlike most deltas, its waters do not flow into an ocean but instead spread across the desert sands, forming an expansive network of channels, lagoons, and islands. Its annual flooding cycle counter-intuitively occurs during the region’s dry winter season. This annual inundation breathes life into an otherwise parched landscape, supporting an exceptional array of biodiversity.
The Source and Journey of the Floodwaters
The floodwaters that sustain the Okavango Delta originate in the Angolan highlands from the Cubango and Cuito rivers. These rivers swell with heavy summer rains, typically between January and February. The Cubango River, known as the Okavango River in Botswana, begins its journey in Angola’s sandy highlands.
The water then travels over 1,000 kilometers (620 miles) through Namibia before reaching Botswana. The surge from the Angolan rains takes about one month to travel the first 1,000 kilometers of the Okavango River. The water then continues its slow, meandering path for another four months to filter through the delta’s intricate network of channels and floodplains. This travel time explains why the flood arrives in Botswana months after the Angolan rainy season.
The Annual Flood Timing
The annual floodwaters typically begin arriving in the Okavango Delta’s Panhandle region, the northernmost part, around April or May. This initial influx marks the start of the delta’s transformation, as water levels gradually rise and expand across the landscape. The flood peaks between June and August, extending into September in some areas. This timing is notable because it coincides with Botswana’s dry winter months, a period when local rainfall is minimal.
During its peak, the delta can swell to three times its permanent size, expanding from 6,000 square kilometers to between 15,000 and 22,000 square kilometers. Water levels begin to recede from August onwards, with a noticeable decline in October. By the end of the dry season in November, the floodplains shrink, leaving only the deeper pools and main channels.
Factors Shaping the Flood
The magnitude and duration of the Okavango Delta’s annual flood are influenced by several factors. The amount of rainfall in the Angolan highlands directly impacts the volume of water flowing into the Okavango River system. Evaporation and transpiration across the delta’s vast, shallow floodplains and channels play a significant role in water loss. High temperatures within the delta contribute to this rapid water loss.
The delta’s geological features also shape the flood’s progression. Ancient fault lines beneath the desert surface dictate the water’s path and slows its flow. Sediment accumulation and shifting peat beds and lagoons continuously divert and alter the speed at which the water travels. This flat gradient, where the river drops only about 60 meters over 250 kilometers, is another reason for the flood’s slow movement across the delta.
Ecological Impact of the Flood
The arrival of floodwaters during Botswana’s dry season holds ecological significance for the Okavango Delta. This timing provides essential water and nutrients when other water sources in the surrounding arid landscape are scarce. The influx of water revitalizes the ecosystem, transforming dry plains into temporary wetlands.
This seasonal abundance of water supports a diverse array of wildlife. Animals migrate back to the delta as other waterholes dry up, leading to a high concentration of wildlife. The floodwaters are crucial for the breeding cycles of aquatic species, with many fish spawning in newly inundated areas. Expanded floodplains and channels attract herbivores and predators, enhancing feeding and hunting opportunities and contributing to the region’s biodiversity.