Why Okavango Delta is drying - experts speak

Exactly 100 years since Batawana’s first relocation after settling in Ngamiland, Maun is staring at the worst drought in recent history. It is not just Maun. The entire south western part of the Okavango Delta is as dry as a bone. 

The annual flood from the Okavango’s catchment was at its lowest levels this year. The low water found empty rivers and it is unlikely that the trickle will reach Maun this year. 

If we were still in the 1800s, Kgosi Kealetile Moremi would be relocating from Maun now.

Historical records show that in 1820 Kwebe, the first capital of Batawana, located on the foothill of Kwebe Hills and peripheries of Lake Ngami, dried up forcing the then Kgosi Moremi to move to Namanyana, which is the current day Toteng.  After Toteng there were many relocations - to Tshoroga, back to Toteng, then Tsau, before a final settlement in Maun in 1915.

These relocations were mainly due to droughts (drying of rivers) and natural disasters involving diseases such as Rinderpest.

Most of the Batawana royal settlements (Mauns) were concentrated on the western part of the Okavango Delta and around Lake Ngami that was fed by the Thaoge River.

Thaoge River is one of the three main splits of the Okavango Delta. Others are the Nqoga – Maunachira – Khwai and the Jao – Boro systems. The Thaoge River flow into Lake Ngami died in the mid-1900s. Is the Jao-Boro system next on the line, especially looking at its current state?  Is the Okavango Delta dying?

Mmegi invited experts, who have extensively worked on the Okavango River Basin to explain the status of the current water levels.

Record lowest rainfall

The first thing that experts highlighted is that the entire Okavango River Basin – from Cuito in Angola to Makgadikgadi in Botswana, has received the lowest rainfall on record since the infamous 1981 drought. That means it is lower than the 1995-96 drought, when Mohembo received the smallest annual inflow on record.

The data from Hydrological Services Namibia’s flood bulletin confirms that the 2018-2019 rainy season was one of the driest in 38 years. The bulletin reports that most of the catchment of the Okavango River Basin was this season characterised by “lower than normal rains due to delayed and erratic onset of rains”. 

According to data from the Hydrological Services Namibia, the Okavango River in Rundu (located in Caprivi before the water enters Botswana) peaked at 5.16m in February and water levels remained the lowest as compared to over the past five years. In May the flood had already subsided to 4.29m, which is considerably lower from 2018’s 5.35m level.

Why is this happening now?

Dr Piotr Wolski, chief research officer (hydro-climatology) from University of Cape Town argues that the Okavango River Basin is going through a normal trend.

“This year does not come from nowhere. It is a result of the overall recent drying or a ‘trend’, if you like that is manifesting after the high flows of the 2010. The interesting aspect there is the fact that a similar ‘trend’ was there in between the 1980s and 1990s. In the meantime, we’ve had opposite ‘trend’ or wetting between the mid-1990s and the 2010,” argues Wolski.

Wolski maintains that, “This is all part of what we call a multi-decadal variability in regional climate, likely linked to processes such as Pacific Decadal Oscillation or similar, which are essentially large scale anomalies in sea surface temperatures”.

Dr Judith Maryna Storie calls it the earth breathing cycle.  She posits: “The earth ‘breathes’ and this means sometimes ‘breathing in, holding breath and then breathing out again’. A dry spell sometimes accompanied by severe drought is part of the ‘breath cycle’”.

Dr John Mendelsohn shares the same sentiments of low rainfall, but adds that the situation is exacerbated by Cuito and Cuando ‘sponges’.

“This season’s low rainfall comes on the back of several recent years of below normal rain in the catchment, which means that sponges and seeps the catchments may be less saturated than usual. These sponges are most evident in the catchments of the Cuito and especially the Cuando (Kwando), and so the Cuando and Linyanti may be very low as a result over the next couple of years,” Mendelsohn argues.

According to the National Geographic Okavango Wilderness Project (NGOWP) 2018 report on the Initial Findings from Exploration of the Upper Catchments of the Cuito, Cuanavale and Cuando Rivers in Central and South-Eastern Angola, these ‘sponges’ are the ‘glaciers’ of the system.

“All source lakes, seepages, high-altitude bogs, and upper reaches of the rivers are adjoined by ancient stratified peat deposits that serve to hold huge amounts of water.

These vast seepage systems depend on high rainfall on the Bié Plateau, deep Kalahari sand deposits, and the Miombo woodlands to create favourable microclimates, restrict the spread of fire, store water and carbon, and maintain a mist belt between 1,200 and 1,500 metres above sea level. This giant sponge, as the ‘water tower’ of south-central Africa, slowly and reliably releases water into these important river systems just as a glacier can do in other ecosystems,” the NGOWP report said.

Wolski, however, provides a different perspective on the role of the sponges in the upper catchment area of the Okavango.

He presents that: “The ‘sponges’ [they] are talking about actually play the opposite role to what [they] suggest. They do not store water for the downstream flow. That water is stored in groundwater. They lose seeping groundwater to evaporation, very much like the well described highveld dambos in Zimbabwe and Malawi do. That the ‘sponges’ or upstream wetlands are dry is a result of low groundwater recharge in the last couple of years.”

Is this result of Climate Change?

Researchers disagree that the current drying of the Okavango Delta is due to the climate change’s phenomenon.

Storie argues that it is indeed ‘climate change’ but she rather prefers to call it ‘climate variation’.

“The Greenhouse gasses emissions will not reduce soon enough to stop the wave of impacts that we are already facing. It will only get worse and it cannot be halted any longer. Increased temperatures, heat waves, more variable rainfall patterns – and all the other known results are inevitable,” she says.

Storie also warns saying, “we have to adapt and change the way we live, if we are to survive the climate variability which is simply going to increase in intensity”.  Wolski on the other hand does not fully agree that Okavango Delta’s situation is due to climate change.

“Is what we see at the moment a result of climate change? It is not very likely. I think we mostly see the effect of decadal climate variability. I don’t think the recent decline in rainfall and this year’s rainfall being the lowest since 1981 is the effect of climate change.

Climate change might have played a role in the recent trend, but it was minimal at best. It might have played a role in the lowest rainfall, but again, it was likely minimal. However, the effect of low rainfall is likely exacerbated by the increasing temperatures. Both in the catchment, and very likely more strongly in the Delta and Maun,” Wolski argues.

Professor Paul Skelton from the South African Institute of Aquatic Biodiversity also argues that the current drought is unlikely due to climate change.

He says, “there are natural cycles to be considered, but overall climate change is an insidious shift that will be measured over a longer period - so this year’s drought is not likely to be a sudden ‘climate change’ matter”.

Is the Okavango Delta dying?

Although Storie said this was just a breathing cycle, she has low hope for the Okavango Delta. She urges everyone and everything to start to learn to adapt.  “As far as I am concerned, the Delta will never ‘return to what it was before’,” says Storie.

“What we see now should be considered to be the new norm. We urgently need to change and adapt our ways to take cognisance to and adapt to this new norm. Downstream, we need to adapt and manage if we are to have any hope of getting through this alive. Unscathed not, unchanged, not. Let’s face the new norm and help our villages and communities to work with the new norm.”

Wolski has hope and confidence on the return of the Delta. He even warns of coming floods.

“It is not likely that the recent trend is the ultimate trend, i.e. that it will continue unabated until the Delta does not receive any water at all. It is most likely that this trend will get reversed. We will get into a phase of progressive wetting, and we will have floods of similar magnitude to those in the early 2010s and 1970s,” he says.

The tricky part, he says, is to tell when. As well as to tell how long will the dry phase last.

“It is tricky, because those multi-decadal fluctuations are not very regular in the first place, and secondly, their influence is modified by many factors at shorter time scales, like a simple year on year variability,” says Wolski. Mendelsohn goes even further to argue that in fact this current drying is important to the existence of the Delta.

“The periodic drying (and burning) of parts of the Delta is needed to release nutrients bound-up in plant material, otherwise the whole Delta would be covered in permanent and rather sterile swamps. The book Okavango Delta - Floods of Life, shows that the periodic drying and wetting of the Delta are both (perhaps even equally) important for its biological productivity.”

*This report was made possible by Mmegi with special thanks to the National Geographic Okavango Wilderness Project.