SKUKUZA – Across the central and eastern Pacific, there is a constant interplay between the temperature of the ocean and the atmosphere. It is referred to as the El Niño-Southern Oscilation (ENSO) cycle. Sometimes, the temperature fluctuates higher or lower than the norm, affecting weather and climate across the globe. Simply put, a cold-ocean water phase is referred to as La Niña. Currently, we are in a warm phase, better known as El Niño, which typically reaches its peak from December to February. In one corner of South Africa, conservationists are keeping an interested eye on El Niño. The most recent data from the National Oceanic and Atmospheric Administration (NOAA) in the United States indicates that this phase is likely to continue into our summer-rainfall months. Should this be the case, it could hold far-reaching consequences for South Africa’s most famous conservation area – the Kruger National Park (KNP). Climatic conditions such as these indicate a strong possibility of severe drought.
Already, the rainfall of the summer of 2014/15 was below normal across large parts of the park and catchment areas of the five perennial rivers that run through it. The Luvuvhu, Letaba, Olifants, Sabie and Crocodile rivers all originate outside the park, flowing from west to east through the protected area, then Mozambique, and eventually drain into the Indian Ocean. South Africa’s most iconic park is no stranger to drought conditions. But when your animals have nowhere to migrate to when rivers and pools dry up, you need to come up with a mitigation plan.
The impact, should this happen, is unknown. The previous time that the park experienced severe drought was during the 1991/92 cycle, and the consequences still ripple through policy and management plans more than 20 years later. And, should a severe drought take place, it would be in an environment where conservation principles have changed considerably. The consequences this time around will only be clear in retrospect. In preparation, South African National Parks (SANParks) and KNP management are bracing themselves for the worst while keeping a window of opportunity wide open for the knowledge they are expecting to gain from the event.
Also see: The drought is far from over
The mean annual rainfall (MAR) in the KNP varies from approximately 740 millimetres at Pretoriuskop in the south to about 440 at Pafuri in the north, but during droughts or floods rainfall can vary from 50 per cent below or 50 per cent above the long-term average respectively. Naturally, there are cycles of high and low rainfall, seen as drivers to healthy ecosystem functioning such as weaker animals dying off, leaving a genetically stronger population. However, large infrequent disturbance events (LIDE) such as extreme droughts or floods, are different altogether. It could cause severe or longer term ecosystem changes, especially since the ecosystem of a conservation area like the KNP is curbed by fences, and the rivers that run through it are heavily utilised before they enter the park. Therefore, should a LIDE be on the cards, management steps in. A number of provisions are already being made in the park. Park management has had a number of severe droughts in the KNP’s existence to learn from; in the 1960s and early 1970s and then again predominant droughts from about 1982 to 1997. According to Dr Eddie Riddell, the park’s manager of freshwater resources, “The most recent and well-documented droughts in the Kruger National Park is that of 1991 to 1992 when the park received only 44 per cent of the long-term average rainfall from a 100-year record.” The El Niño-related droughts of 1982/83 and 1991/92 were the most severe droughts on record in the KNP and large parts of the rest of southern Africa. Both these events were characterised by below-normal rainfall for two consecutive years – a situation predicted for this year, says Dr Freek Venter, Kruger National Park conservation general manager.
During the 1991/92 drought, Kruger’s 30 000-strong buffalo population shrank by about 60 per cent to 14 000
A severe drought such as that experienced in 1991/92 holds many consequences – near inconceivable to those that have not experienced it before. In March 1992 the Sabie River, generally regarded as the most biodiverse in South Africa, was near to losing its status as a perennial river for the first time in recorded history.
Major water users in the catchment came together, eventually forming the Sabie River Working Group (SRWG), consisting of irrigation farmers and forestry and state departments.
Farmers voluntarily restricted irrigation up to 60 per cent and forestry ringbarked hundreds of stray trees along the banks of the river, preventing the Sabie from drying up. Inside the park, the 30 000-strong buffalo population shrank by about 60 per cent to 14 000 and many other herbivore population numbers declined, including hippo, warthog, common reedbuck, kudu and giraffe. Rare antelope such as roan, sable, eland and tsessebe also declined significantly.
According to Venter, many of these animal populations rebounded in the wet years that followed, though rare-antelope numbers remain low.
Looking back, moving forward
Since then, a number of changes has taken place in the park. The 1991/92 drought was one of the most researched and documented, says Riddell. “We know that these dry periods change the balance in favour of the plains game such as zebra and blue wildebeest which utilise the shorter grasses, while not favouring those long-grass feeders such as buffalo and the rare roan, tsessebe and reedbuck.”
This, in turn, leads to a switch in the grass species composition of the veld due to the resulting grazing pressure dynamics, he says. “We also know that the larger predators, such as lions, leopards and hyenas, did well during these times, at the expense of the smaller predators, including wild dogs, cheetahs and jackals by out-competing them for resources.”
Furthermore, the surviving buffaloes were the strongest and most resilient, and thus only the “best” repopulated the park. Significantly, management started looking differently at the water-provision strategy in the park. In the past, waterholes were steadily increased from 1911 until the 1990s to provide reliable water in an environment that was perceived to be “drying out”.
They reached a peak of about of 300 and included catchment dams in seasonal streams. Current guidelines include that water should not be provided in areas that are naturally dry, or be provided too evenly across the landscape. Water provision is still condoned in certain areas to cater for tourist expectations and because of remaining fences (inhibiting a complete return to natural water availability).
However, for the most part, artificial water points are being closed down, certain dams breached and rehabilitated and in a few relevant cases water points opened up again. In effect, vegetation and animal distribution patterns are allowed to recover so that seasonal variation between times of water availability and drought can fulfil their natural function.
A common misconception is that animals die of thirst during prolonged droughts when, in fact, most starve to death after grazing has been depleted, explains Riddell. It is therefore important to provide water in a way that creates conditions suitable for sustaining a wide range of biodiversity, and not only for those species that do better in close proximity to water (like zebra and blue wildebeest). Thus those species that prefer to occupy drier areas further from water where there are fewer predators, less competition for food and less trampling (like sable and roan antelope) also need to be catered for.
The KNP’s new water-provision policy creates refuge areas for grass further away from permanent water. The aim is for seasonal variation in water availability and drought episodes to again fulfil their natural function in the system.
KNP will have a number of other weapons in its arsenal to offset potentially catastrophic effects of a severe drought, this time around. Following the 1991/92 drought, the SRWG successfully lobbied the former minister of water affairs, Mr Kader Asmal, for additional storage capacity in the catchment, which led to the construction of the Inyaka Dam on the Marite River tributary of the Sabie.
Venter says this process created an outstanding relationship with and awareness among water users in the Sabie River catchment that lasted for more than a decade.
“From these droughts also flowed the 12-year-long WRC-funded KNP Rivers Research Programme, involving many scientists from several universities, that was designed to inform minimum in-stream flows and water quality for KNP rivers. Knowledge gained from this programme eventually cascaded into the Environmental Reserve clause of the National Water Act.”
This does not mean that substantial challenges do not remain.
“There have been some challenges of late to meet the ecological reserve in the catchments of the Letaba, Crocodile and Sabie rivers,” says Riddell.
These issues have been resolved through collaboration with upstream institutions particularly catchment-management agencies and water-user associations as well as the Department of Water and Sanitation.
As a result, the ecological reserve could be met due to water releases from dams (the Tzaneen, Kwena and Inyaka dams respectively). He says if the dry period continues for another year or two, reconciling the rivers’ ecological reserve requirements with those of upstream users will become more challenging.
Venter adds that census numbers of large herbivores in the KNP indicate that the biomass of these animals has more than doubled during the past decade. This increased animal biomass (most of it due to an increasing elephant population) may have compounding effects on the influence of the next major drought.
Still more questions than answers
While ENSO can be forecast with good skill up to nine months ahead, it is critical to keep in mind that an El Niño/La Niña forecast is not a rainfall forecast. Though most El Niño years have been associated with below-normal rainfall, this impact is often reduced by sufficient groundwater and soil-moisture content that have remained in the system from previous season.
It is complicated further by the fact that the numerous rainfall regions in southern Africa correlate differently with ENSO. It cannot be accepted as a rule that the southern part of Africa will receive below-normal rainfall during El Niño years and above-normal rainfall during La Niña. For example, according to Weather SA, “The 1997/98 El Niño was the strongest on record, but not all of South Africa received below-normal rainfall.
“Some regions had an abundance of rain because of moist air that was imported from the Indian Ocean.”
For KNP management, this implies that it will have to wait for the rain or the lack thereof, to make any concrete conclusions. For any answers, we will have to wait for something as fickle as the weather.
