Why lakes in the Rift Valley are rising at alarming rate

It is a deluge that has puzzled not only Rift Valley residents but also Kenyans all over the country.

Thousands have been left homeless and hundreds of thousands others are at risk of being displaced by flooding Rift Valley lakes.

Already, property and infrastructure of unknown value have been destroyed by the floods around lakes Naivasha, Nakuru, Baringo, Bogoria and Turkana.

Residents are now living in fear after researchers said the situation may not get better any time soon as water is rising by the minute.

Lake Turkana, for instance, has risen to unprecedented levels in decades. The floods have displaced at least 24,000 people in the past few months.

The lake is fed by Rivers Turkwel and Kerio from Mt Elgon and River Omo from the Ethiopian highlands.

Data shows Lake Turkana has risen by 300m to the current 800m in the recent months. Such high levels were last witnessed in the1970s and early 1900s. In 1896 it was at 814.6m. “While this shows that the levels aren’t unprecedented, today all of Kenya’s Rift Valley lakes face modern challenges arising from growing infrastructure development pressures,” said Sean Avery, a chartered consultant in Hydrology and Water Resources in Quartz Africa.

This damage has been made worse by the fact that Lake Turkana is connected to the Turkwel Gorge Dam, which at the moment is almost overflowing. The dam is threatening the lives of more than 300,000 people downstream, according to the Water Resources Authority (WRA).

Villages submerged

As of October 19, this year the dam, whose capacity is 1150m above sea level, was 1148m full. With the current rains, the dam is expected to overflow later in November, WRA has projected.

The other lakes on the floor of the Rift Valley have also risen to levels not seen in more than five decades. They started to rise in 2010 and have not stopped since. Current satellite images and expert studies show an overflow.

Prof Simon Onywere, the Kenyatta University Capacity Development and Consultancy Services director, sought to find out the overflow levels of the lakes.

In his study, he established that from January 2010 to December 2014 the lakes showed a drastic but consistent increase in water volume, which flooded riparian areas, affecting infrastructure and biodiversity.

He also picked images of the lakes for December 2010 and December 2013 so as to compare water levels. He established that the flooding around Lake Baringo increased from 143.6 square kilometres in January 2010 to 219.8 square kilometres in December 2014. In 1972, Lake Baringo’s maximum depth was nine metres but this decreased to a maximum of four metres in 2002.

But, between 1973 and 2000 the lake decreased by 16 per cent in almost three decades.

According to Prof Onywere’s study, villages around the lake were the casualties of an overflowing lake as all areas below the 980-metre contour line got submerged and remained so. Kokwa dispensary was submerged between 2010 and 2014. Eight schools and seven villages also went under water.

By 2013, the water had crossed Loruk, but had not crossed the road while Lake Baringo Lodge, Soi Lodge and Roberts Camp were under water.

Now, more than 88 square kilometres of land around Lake Baringo and more than 200 hectares of the Pekerra Irrigation project are submerged, he told HealthyNation.

The flooding on Lake Bogoria then was not as intense as it lies in a deep depression. Prof Onywere found that Lake Bogoria’s flooded area rose by 24 per cent between January 2010 and December 2014 while around Lake Naivasha it was almost 50 per cent.

According to WRA, it was in May 2020 that Lake Naivasha reached its highest level since 1932. “Lake Naivasha is 1.4 vertical metres short of the official riparian boundary. In 1917, the lake was 2.4m higher while in earlier centuries, it was 13m higher,” said Dr Avery.

On the other hand, Lake Nakuru saw a significant rise of 77 per cent in the same period. “Lakes Nakuru, Bogoria and Baringo have also risen to their highest levels in decades, inundating roads and building infrastructure, yet they also are not as high as they were in the early part of the last century,” said Dr Avery.

Between December 2013 and 2014, however, lakes Bogoria and Naivasha declined slightly by 0.7 per cent and 2.3 per cent respectively.

But why are the lakes rising?

While numerous people do not seem to understand why exactly these lakes are rising simultaneously to levels not seen in decades, Prof Onywere says the only way to understand them is to know the historical perspective of the rising waters. “The lakes were drying up in January 2010, they had completely receded due to the 2009 drought,” he said.

It then started raining in October 2010, which continued during the 2011 March-April-May season and the lakes were revived. More rain was witnessed in 2012, 2013 and 2014 during each of the rainfall seasons, adding some water into the lakes.

Therefore, the lakes have been rising for the past 10 years, said Prof Onywere.

Some scientists have argued that the Great Rift Valley is shifting. They say it is opening up further as the Somali plate, where Kenya is located, and the Nubian plate (the rest of Africa), move away from each other. It is also prone to volcanic activities, tensional and compressional forces associated with its formation.

In a previous interview, Dr Silas Simiyu, a seismologist and former chief executive of the Geothermal Development Company, said: “Scientifically, the rise in the water level of the lakes in Rift Valley is due to effects of regional tectonics influenced by the movements of global earth’s plate tectonics.”

He explained that the movements create compressional and tensional stress fields, which he associated with the rising lakes.

Heavily silted

But, David Adede, a geotechnical consultant, did not think this is the explanation behind the rising lakes. “There has been a lot more rain than usual. The lakes are also silting and it could be that the soil is displacing water,” he said.

HealthyNation has established that the rise of the lakes could be as a result of many factors.

For example, Dr Avery measured up to 30m of sediment accumulated within Turkwel dam’s reservoir since 1991.

In the case of Lake Nakuru, for example, decades of solid pollution as Nakuru town grows, could be a contributing factor.

Also, the lake’s catchment area - the Mau Forest - has been destroyed through years of deforestation. The forest cover around the lake has declined to below 20 per cent in the past 50 years, from 70 per cent, according to various studies.

Jomo Kenyatta University of Agriculture and Technology’s Mark Boitt, in his 2016 study, established that forested areas around Lake Nakuru reduced to 13 per cent in 2010.

As a result, there has been increased runoff during rainfall and the consequent siltation and sedimentation of the lake, which does not have an outlet. Satellite images of all the lakes show that rivers feeding them are beige in colour, meaning they are greatly silted. Examples are River Malewa and River Ndarugu (Njoro), which feed Lake Naivasha.

Lake Bogoria suffers a similar fate, with one tip being totally silted. “A lot of silt has made the lakes shallow. Were it not for the silt, the water level most probably would not be where it is,” said Prof Onywere.

River Omo, which forms 90 per cent of Lake Turkana’s water, joins the lake from the Gigel Gibe III Dam in Ethiopia. From the images, silted water from below the dam’s wall can be seen erupting into the river before finding its way into the lake. “It has been raining very much in the highlands west of the Rift Valley. It has also been raining in the Ethiopian highlands,” he said.

Given that other lakes in the region such as Lake Victoria are also flooding, the phenomenon may not be unique to the Rift Valley lakes.
Climate scientists say the lakes are rising due to increased precipitation over the region.

Dr Avery said he has been doing research which shows there has been above-average annual rainfall over the last decade. “With persistent rainfall, the catchment surface layers saturate, resulting in extended flood periods,” he argued.

Global warming

The Kenya Meteorological Department (KMD) has been researching the issue for some time and has come to the same conclusion.

Dr Richard Muita, the assistant director Public Weather Services at KMD, said: “The issue has been happening for a while. Explanations are different, but the most common is the tectonic movements. But, this is a climate-related issue. Occurrences of precipitation in the last several years have been increasing. The lakes have been rising because of the consistent rainfall from 2015,” he said.

He explained that the hydrological cycle, in which increased precipitation, evaporation and condensation bring about rain, is at play around the Rift Valley lakes. “We have established a trend in our analysis. We looked at the duration of rainfall and the amount over the past several years and made sense of the relationship between the rain and the rising waters in these lakes,” he said.

The researchers looked at rainfall amounts in the highlands west and east of the valley and found there was a positive correlation between rainfall and the rising lakes.

KMD established there was a rainfall concentration around the lakes in the study carried out on lakes Baringo and Naivasha.

Dr Muita explained that there were more of climate variability footprints than climate change.

But there are drivers of the rainfall which are at play too, he said. These include the Indian Ocean Dipole and El Niño-Southern Oscillation, both of which have been fluctuating and causing heavy rainfall over the region.

When the Kenyan Coast is warm, the condition brings a lot of rainfall in the inland and the warming of the Pacific Ocean also brings a lot of rain in the region. These two are as a result of global warming, an aspect of climate change.

Climate change is associated with human and natural activities. Due to these, there have been the growth of greenhouse gases which have consequently warmed the globe. This warming, on the other hand, is influencing Indian Ocean Dipole and El Niño-Southern Oscillation which when positive bring a lot of rain in the region.

Historically, all East African lakes flooded between 1961 and 1964. During this period, there was El-Nino, the same phenomenon which was observed in 2015.

In 2019, the Indian Ocean Dipole was positive in the western Indian Ocean (Kenyan coast). This resulted in enhanced rainfall across the country, the highest to be recorded in decades.

50 year cyclic climatic event

In between these major rainfall incidents - El-Nino and the Indian Ocean Dipole - there have been episodes of above average rainfall, between 2010 and 2020, all which have been contributing volumes of water into the lakes.

According Kenya Meteorological Department, all stations in the country recorded above 125 per cent of the October-November-December long term mean during the 2019 short rains.

This means more water was added into the lakes. “The season made a major contribution to a rapid rise in Lake Victoria’s water level and a combination with above average rainfall during the 2020 long rains led to record breaking water level,” wrote Caroline Wainwright in a research article on Royal Meteorological Society.

“The flooding suggests the presence of increased and constant moisture availability and signifies a return of a 50 year cyclic climatic event,” stated researchers in a publication, the Geomorphology and Society.

According to Adede, there could be other factors leading to the rising waters. These could involve recharge and discharge of water into and from the lakes, but studies are needed to establish it.

Except Lake Naivasha and Lake Baringo, all the other Rift Valley lakes are salty, because they lack outlets. It is suspected that water flows in and out of these lakes through underground channels. “These lakes are generally small and endorheic (closed), with no outflow and are dependent on the balance of inflows and evaporation,” said Prof Onywere.

They are also shallow (Baringo and Nakuru) and very sensitive to any change, whether driven by climate or human activities, he said.
Unfortunately, there is no quick fix to this problem and people have to learn how to relate with the environment, said Adede.