Alarm at mysterious rise in Lake Nakuru water level

…After breakfast we set off to make history by becoming the first living people to cross the lake on foot… There’s no water at all in the lake now.
– Nellie Grant in Elspeth Huxley’s Nellie: Letters from Africa.

 
Whether Elspeth Huxley’s mother was the first person to cross Lake Nakuru on foot is questionable. What we can be certain of, though, is that 74 years ago the lake was completely dry.

And 70 years later, in 2009, an article published by the BBC titled: “Kenya’s heart stops pumping” illustrated a similar scenario — the lake was almost bone dry. “This isn’t the lake shore,” one of the wardens said. “It’s the lake floor.” The situation today, however, is very different.

The water level is the highest it has been for half a century. It’s so high that a considerable portion of Lake Nakuru National Park is submerged, and so too in fact is part of the KWS building at the park’s entrance.

When I visited recently, the lake had swallowed up a section of the northern route, and had flooded a large part of the acacia forest to the south. The network of tracks that once scarred the lakeshore has disappeared, and the roads lead straight into the lake instead. And it’s a similar story for some of Kenya’s other Rift Valley lakes — the water levels of both Lake Naivasha and Lake Baringo are abnormally high.

Though these fluctuations are commonly attributed to seasonal variations in rainfall, it is clear that the climate forms only part of a host of factors affecting the level of the water. Understanding these factors, and their consequences, is crucial for the balance of an ecosystem that is upset by the slightest of climactic or other external variations.

The most obvious factor, you would think, is rainfall — something that Nakuru has become very familiar with of late. According to Abraham Changara, the Kenya Meteorological Department’s principal meteorologist, the level of rainfall in Nakuru has been abnormally high, particularly in the months preceding the annual long and short rains.

July and August this year, for example, received approximately 85mm more rain than during the same period last year.

Apart from directly increasing the volume of water in the lake, high levels of precipitation reduce the average temperature of the lake surface, inhibiting evapotranspiration — which, as it turns out, is the lake’s only output of water.

Lake Nakuru lies at the lowest point of a basin that is fed by five seasonal rivers — Njoro, Makalia, Nderit, Naishi and Larmudiak — which flow from either the Mau Escarpment or the Aberdares. This means that the water level in the lake is influenced more by rainfall in the Mau Forest and on the Aberdare Range than by rainfall in Nakuru itself.

The Mau Forest receives an average of between 1,000 and 2,000mm of rainfall a year, and provides water for 12 seasonal rivers, which feed into six lakes, including Lake Nakuru. It is surprising, then, that the Kenya Meteorological Department doesn’t have a station in the Mau Forest — the largest catchment area in the country — and the closest station to the Aberdares is in Nyahururu.

Although data is hard to come by, the fact that these “seasonal” rivers have been flowing all year is a reflection of the amount of rainfall that these highlands have received.

Precipitation, though, forms only part of the story. The Mau Forest acts as a buffer zone: it rations rainwater during the long rains, and releases it slowly in the dry season. This is why the level of water in Lake Nakuru is normally lower during the rainy season.

In the 15 years up to 2009, however, 100,000 hectares (a quarter of the protected forest reserve) was cleared and settled on. The area lost its ability to retain water, the seasonal rivers dried up, and it triggered one of the worst droughts on record.

Rivers as far south as Narok, and the almost perennial Ewaso Nyiro in Samburu in the north, dried up, and Lake Nakuru itself was only a metre deep. Since then, however, an estimated 40,000 hectares of forest have been rehabilitated by the Kenyan government, and according to the director of the Kenya Water Tower Agency, 10,000 of the forest’s inhabitants have voluntarily surrendered their title deeds to aid this rehabilitation.

One would think, though, that it would take longer than four years for this conservation initiative to take effect — for the newly planted trees to once again retain rainwater and act as an efficient buffer.

To shed light on the issue, I approached the Kenya Wildlife Service’s senior scientist for wetlands, Dr Judith Nyunja, whose team of researchers has kept a close eye on hydrological developments in Nakuru.

“Conservation in the catchment goes beyond just replanting trees. It is also about the ability of the soils to capture water. So as well as afforestation, local farmers have been trained to use proper, less destructive, farming methods.”

Her research has also pinpointed siltation as another reason for the high water level in Lake Nakuru. As soon as the seasonal rivers started flowing again, they picked up loose soil from the deforested slopes of the Mau Escarpment and deposited it in the lake. This build-up of sediment raised the lake floor, which caused it to flood once the water flowed in.

Interestingly, though, Dr Nyunja believes that the main cause of the high water level is geological. She believes that an undiscovered flow of groundwater connects, and is feeding, Lake Naivasha, Lake Nakuru, Lake Bogoria and Lake Baringo. The only known permanent inlet to Lake Nakuru is the Baharini spring on its eastern shoreline which, it has been found, only contributes about 0.6 cubic metres of water per second.

So where is this other mystery source of groundwater? To find out, Dr Nyunja is planning a trip to the shores of Lake Nakuru next month with a multi-disciplinary team of Kenya’s finest hydrologists.

Considering that the fluctuations in the water level of all the lakes seem to be synchronised, it wouldn’t be surprising if a new groundwater inlet were uncovered. And the fact that the massive aquifers in Turkana were only just discovered illustrates how easy it is to overlook crucial groundwater systems. Until then, though, it remains speculation.

Consequences

Though the true cause of the high water level of Lake Nakuru may be unclear, its consequences for the ecosystem are unquestionable.

The most obvious being the lack of Lesser Flamingos, which have flown in their tens of thousands to Lake Bogoria. The flamingos feed off blue-green algae, or cyanobacteria, which thrive in alkaline water.

The water in Lake Nakuru is now too deep, and not saline enough, to support the growth of the algae.

This dilution inhibits the reproduction of the lake’s Tilapia, which larger water birds and birds of prey feed on. The lake’s shoreline was also a crucial breeding site for a number of birds, including the Kittlitz and Blacksmith Plovers. 

Habitat constriction is another problem, particularly for the population of buffaloes, which was even deemed too large for the national park before the lake started to expand.

According to Nigel Hunter, former director of the East African Wildlife Society, a considerable number of buffaloes will have to be relocated to other parks.

The saline water has also flooded and dehydrated large parts of the acacia forest, which is forcing its inhabitants — like leopards, which are extremely territorial — to occupy a much smaller space. And the same can be said for the park’s tourists.

Though Sarova Lion Hill claims that the number of guests is still high, the flooded roads are undoubtedly a deterrent. Large parts of the park are inaccessible, and even those that are can only be reached in a 4x4.

Dr Nyunja’s project, then, has come at a very crucial time for the Lake Nakuru ecosystem. As well as that research, a conference on the Rift Valley lakes has been scheduled at the KWS Training Institute in Naivasha from the December 3 to the December 6.

The fact that we are still debating why the lakes are so high, even though the water levels have been fluctuating drastically, shows that we don’t quite yet fully understand the dynamics of this complex hydrological system.

Hopefully this will soon change, not just for Lake Nakuru National Park, but for the balance of Kenya’s Rift Valley ecosystem as a whole.