Wikipedia

Okavango Delta

TheOkavango Delta[2](orOkavango Grassland;formerly spelled "Okovango" or "Okovanggo" ) inBotswanais a vastinland deltaformed where theOkavango Riverreaches atectonic troughat an altitude of 930–1,000 m[3]in the central part of theendorheic basinof theKalahari Desert.

Okavango Delta
UNESCO World Heritage Site
Map of the delta withbasinboundary as dashed line
LocationBotswana
CriteriaNatural: vii, ix, x
Reference1432
Inscription2014 (38thSession)
Area2,023,590 ha
Buffer zone2,286,630 ha
Coordinates19°24′S22°54′E/ 19.400°S 22.900°E/-19.400; 22.900
Official nameOkavango Delta System
Designated12 September 1996
Reference no.879[1]
Okavango Delta is located in Botswana
Okavango Delta
Location of Okavango Delta in Botswana
Satellite image (SeaWiFS) of Okavango Delta, with national borders added
Typical region in the Okavango Delta, with free canals and lakes, swamps and islands

It is aUNESCOWorld Heritage Siteas one of the few interior delta systems that do not flow into a sea or ocean, with a wetland system that is largely intact.[4]All the water reaching the delta is ultimatelyevaporatedandtranspired.Each year, about 11 cubic kilometres (2.6 cu mi) of water spreads over the 6,000–15,000 km2(2,300–5,800 sq mi) area. Some flood waters drain intoLake Ngami.[5]The area was once part ofLake Makgadikgadi,an ancient lake that had mostly dried up by the earlyHolocene.[6]

TheMoremi Game Reserveis on the eastern side of the delta. The delta was named one of theSeven Natural Wonders of Africa,which were officially declared on 11 February 2013 inArusha,Tanzania.[7]On 22 June 2014, the Okavango Delta became the 1000th site to be officially inscribed on the UNESCO World Heritage List.[8][4]

Geography

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Floods

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The Okavango is produced by seasonal flooding. The Okavango River drains the summer (January–February) rainfall from theAngolahighlands and the surge flows 1,200 km (750 mi) in around one month. The waters then spread over the 250 by 150 km (155 by 93 mi) area of the delta over the next four months (March–June).

The high temperature of the delta causes rapidtranspirationandevaporation,resulting in three cycles of rising and falling water levels[9]that were not fully understood until the early 20th century. The flood peaks between June and August, duringBotswana's dry winter months, when the delta swells to three times its permanent size, attracting animals from kilometres around and creating one of Africa’s greatest concentrations ofwildlife.

The delta is very flat, with less than 2 m (7 ft) variation in height across its 15,000 km2(5,800 sq mi),[10]while the water drops about 60 m from Mohembo to Maun.[3][11][12]

Water flow

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Lagoons

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Shinde Lagoon, seen from the air

When the water levels gradually recede, water remains in major canals and river beds, in waterholes and in a number of largerlagoons,which then attract increasing numbers of animals. Photo-safari camps and lodges are found near some of these lagoons. Among the larger lagoons are:

Salt islands

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The agglomeration of salt around plant roots leads to barren white patches in the centre of many of the thousands of islands, which have become too salty to support plants, aside from the odd salt-resistantpalm tree.Trees and grasses grow in the sand around the edges of the islands that have not become too salty yet.

About 70% of the islands began astermitemounds (oftenMacrotermesspp.), where a tree then takes root on the mound of soil.[13]

Chief's Island

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Chief's Island (19°12′S22°48′E/ 19.200°S 22.800°E/-19.200; 22.800), the largest island in the delta, was formed by afault linewhich uplifted an area over 70 km long (43 mi) and 15 km wide (9.3 mi). Historically, it was reserved as an exclusive hunting area for the chief, but is now a protected area for wildlife. It now provides the core area for much of the resident wildlife when the waters rise.[14]

Climate

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Aerial view of delta as floodwaters recede, August 2012

The Delta's profuse greenery is not the result of a wet climate; rather, it is anoasisin an arid country. The average annual rainfall is 450 mm (18 in) (approximately one-third that of its Angolan catchment area) and most of it falls between December and March in the form of heavy afternoon thunderstorms.

December to February are hot wet months with daytime temperatures as high as 40 °C (104 °F), warm nights, and humidity levels fluctuating between 50 and 80%. From March to May, the temperature reduces, with a maximum of 30 °C (86 °F) during the day and mild to cool nights. The rains quickly dry up leading into the dry, cool winter months of June to August. Daytime temperatures at this time of year are mild to warm, but the temperature falls considerably after sunset. Nights can be cold in the delta, with temperatures barely above freezing.[15]Frost is sometimes seen over the winter.[16]

The September to November span has the heat and atmospheric pressure build up once more, as the dry season slides into the rainy season. October is the most challenging month for visitors: daytime temperatures often push past 40 °C (104 °F) and the dryness is only occasionally broken by a sudden cloudburst.[17]

Fauna of the delta

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A cheetah silhouetted against a sunset in the delta

The Okavango Delta is both a permanent and seasonal home to a wide variety of wildlife which is now a popular tourist attraction.[18]All of thebig five gameanimals—thelion,leopard,African buffalo,African bush elephantand rhinoceros (bothblackandwhite rhinoceros)—are present.[19]

Other species includegiraffe,blue wildebeest,plains zebra,hippopotamus,[20]impala,common eland,greater kudu,sable antelope,roan antelope,puku,lechwe,waterbuck,sitatunga,tsessebe,cheetah,[21]African wild dog,spotted hyena,black-backed jackal,caracal,serval,aardvark,aardwolf,bat-eared fox,African savanna hare,honey badger,crested porcupine,common warthog,chacma baboon,vervet monkeyandNile crocodile.[22]

The delta also hosts over 400 bird species, including thehelmeted guineafowl,African fish eagle,Pel's fishing owl,Egyptian goose,South African shelduck,African jacana,African skimmer,marabou stork,crested crane,African spoonbill,African darter,southern ground hornbill,wattled crane,[23]lilac-breasted roller,secretary bird,andcommon ostrich.[24]Prime bird-watching areas are those with a mix of habitats such as the panhandle, the seasonal delta and the parts of the Moremi Game Reserve that are close to the water.[25]

Since 2005, the protected area has been considered a Lion Conservation Unit together withHwange National Park.[26]

In 1992, the black rhino was thought to be extinct in the Okavango Delta, while only 19 white rhinos remained.[27]By 1993, all rhinos had been killed in Botswana.[28]Hundreds of white and black rhinos were reintroduced by the Botswana Rhino Reintroduction Project founded in 2000.[28]From 2010 to 2018, seven rhinos were killed by poachers.[29]By 2019, the rhino population in Botswana had decreased to an estimated 400, with the largest population of roughly 150 living in the northern Okavango Delta.[30]From 2020 to 2021, 92 rhinos were killed by poachers in the delta region leaving only 40 individuals, prompting the government to move those rhinos out of the Okavango Delta.[27][31]

Small gathering oflechweantelopes, Okavango Delta

The most abundant large mammal is the lechwe, with estimates suggesting approximately 88,000 individuals.[32]The lechwe a bit larger than an impala, with elongated hooves and a water-repellent substance on its legs that enable rapid movement through knee-deep water. Lechwe graze onaquatic plantsand, like the waterbuck, take to water when threatened by predators. Only the males have horns.[33]

Fish

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The Okavango Delta is home to 71 fish species, including thetigerfish,species oftilapia,and various species ofcatfish.Fish sizes range from the 1.4 m (4.6 ft)African sharptooth catfishto the 3.2 cm (1.3 in)sickle barb.The same species are found in theZambezi River,indicating an historic link between the two river systems.[34]

Flora of the delta

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The Okavango Delta is home to 1068 plants which belong to 134 families and 530 genera.[35]There are five important plant communities in the perennial swamp:Papyrus cyperusin the deeper waters,Miscanthusin the shallowly flooded sites, andPhragmites australis,Typha capensisandPycreusin between. The swamp-dominant species, which are usually found in the perennial swamp, also extend far into the seasonally inundated area.[17]Papyrus cyperusreeds beds grow best in slow flowing waters of medium depth and are prominent at the channel sides. On the islands and mainlands edges above the flooded grasslands different communities of flora are found. These species are located according to their water preference: for instancePhilenoptera violacearequires little water, is found at the highest elevations in the perennial swamps, and is common on drier seasonal swamp islands. Trees restricted to islands within the perennial swamp are a mixture of the palmHyphaenepetersianaandacacias.[35][36]

The plants of the delta play an important role in providing cohesion for the sand. The banks or levees of a river normally have a high mud content, and this combines with the sand in the river’s load to continuously build up the river banks. The river’s load In the delta consists almost entirely of sand, because the clean waters of the Okavango contain little mud. The plants capture the sand, acting as the glue and making up for the lack of mud, and in the process creating further islands on which more plants can take root.

This process is not important in the formation of linear islands. They are long and thin and often curved like a gently meandering river because they are actually the natural banks of old river channels which have become blocked up by plant growth and sand deposition, resulting in the river changing course and the old river levees becoming islands. Due to the flatness of the delta and the large tonnage of sand flowing into it from the Okavango River, the floor of the delta is slowly but constantly rising. Where channels are today, islands will be tomorrow and then new channels may wash away these existing islands.[37]

People

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Hambukushu guide poles hismakoroon delta floodwaters

The Okavango Delta peoples consist of five ethnic groups, each with its own ethnic identity and language. They areHambukushu(also known as Mbukushu, Bukushu, Bukusu, Mabukuschu, Ghuva, Haghuva), Dceriku (Dxeriku, Diriku, Gciriku, Gceriku, Giriku, Niriku),Wayeyi(Bayei, Bayeyi, Yei), Bugakhwe (Kxoe, Khwe, Kwengo, Barakwena, G|anda) and ǁanikhwe (Gxanekwe, ǁtanekwe,River Bushmen,Swamp Bushmen, Gǁani, ǁani, Xanekwe). The Hambukushu, Dceriku, and Wayeyi have traditionally engaged in mixed economies of millet/sorghum agriculture, fishing, hunting, the collection of wild plant foods, and pastoralism.

The Bugakhwe and ǁanikwhe areBushmen,who have traditionally practised fishing, hunting, and the collection of wild plant foods; Bugakhwe used both forest and riverine resources, while the ǁanikhwe mostly focused on riverine resources. The Hambukushu, Dceriku, and Bugakhwe are present along the Okavango River in Angola and in theCaprivi Stripof Namibia, and small numbers of Hambukushu and Bugakhwe are in Zambia, as well. Within the Okavango Delta, over the past 150 years or so, Hambukushu, Dceriku, and Bugakhwe have inhabited the panhandle and the Magwegqana in the northeastern delta. ǁanikhwe have inhabited the panhandle and the area along the Boro River through the delta, as well as the area along theBoteti River.

The Wayeyi[38]have inhabited the area aroundSerongaas well as the southern delta aroundMaun,and a few Wayeyi[39]live in their putative ancestral home in the Caprivi Strip. Within the past 20 years many people from all over the Okavango have migrated to Maun, the late 1960s and early 1970s over 4,000 Hambukushu refugees from Angola were settled in the area aroundEtshain the western Panhandle.

The Okavango Delta has been under the political control of theBatawana(aTswananation) since the late 18th century.[40]Led by the house of Mathiba I, the leader of aBangwatooffshoot, the Batawana established complete control over the delta in the 1850s as the regional ivory trade exploded.[41]Most Batawana, however, have traditionally lived on the edges of the delta, due to the threat that thetsetse flyposes to their cattle. During a hiatus of some 40 years, the tsetse fly retreated and most Batawana lived in the swamps from 1896 through the late 1930s. Since then, the edge of the delta has become increasingly crowded with its growing human and livestock populations.

Flood-control bunds for flood recession cropping in themolapoof the Okavango, Botswana

Molapos(water streams)

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After the flooding season, the waters in the lower parts of the delta, near the base, recede, leaving moisture behind in the soil. This residual moisture is used for planting fodder and other crops that can thrive on it. This land is locally known asmolapo.

During 1974 to 1978, the floods were more intensive than normal and flood recession cropping was not possible, so severe food and fodder shortages occurred. In response, the Molapo Development Project was initiated. It protected themolapoareas with bunds to control the flooding and prevent severe flooding. The bunds are provided with sluice gates so the stored water can be released and flood recession cropping can start.[42]

Possible threats

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One possible threat is oil exploration by Canadian company ReconAfrica. Initial exploration in April 2021 revealed oil deposits in sedimentary rock.[43]Environmentalists are concerned that the project will have a negative ecological impact and that some of the main bodies of water could be threatened.[44][45][46] ReconAfrica has stated, "There will be no damage to the ecosystem from the planned activities."[47][48]

The Namibian government has presented plans to build ahydropowerstation in theZambezi Region,which would regulate the Okavango's flow to some extent. While proponents argue that the effect would be minimal, environmentalists argue that this project could destroy most of the rich animal and plant life in the delta.[49]Other threats include local human encroachment and regional extraction of water in both Angola and Namibia.[50][51]

South African filmmaker and conservationistRick Lombawarned in the 1980s of the threat of cattle invasion to the area. His documentaryThe End of Edenportrayed his lobbying on behalf of the delta.

The Okavango catchment is projected to experience decreasing annual rainfall as well as increasing temperatures as a result of global warming.[52]The effects of global warming are likely to result in reductions in the extent of floodplains in the Okavango Delta, which will have significant impacts on water availability as well as livestock rearing and agricultural activities in the region.[53]

See also

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References

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  53. ^Murray-Hudson, M.; Wolski, P.; Ringrose, S. (2006). "Scenarios of the impact of local and upstream changes in climate and water use on hydro-ecology in the Okavango Delta, Botswana".Journal of Hydrology.Water Resources in Regional Development: The Okavango River.331(1): 73–84.Bibcode:2006JHyd..331...73M.doi:10.1016/j.jhydrol.2006.04.041.

Further reading

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