Floods in Kenya killed at the least 169 individuals between March and April 2024. Essentially the most catastrophic of those deaths occurred after a flash flood swept by a rural village killing 42 individuals. Loss of life and destruction have additionally occurred within the capital, Nairobi, a stark reminder of the persistent failure to maintain abreast of the town’s fast urbanisation wants. Sean Avery, who has undertaken quite a few flood and drainage research all through Africa, unpacks the issues and potential options.
Are floods in Kenya inflicting extra harm? If that’s the case, why?
Floods are the pure consequence of storm rainfall and have an necessary ecological function. They inundate flood plains the place silts settle, riverbed aquifers are recharged and vitamins are gathered. Annual rainfall in Kenya varies from 2,000mm within the western area to lower than 250mm within the drylands overlaying over 80% of Kenya. However storm rainfalls are widespread. Which means that floods can happen in any a part of the nation.
The affect of floods has change into extra extreme as a result of numerous components.
The primary is how a lot water runs off. In rural areas, adjustments to the panorama have meant that there’s been a rise within the quantity of storm runoff generated from rainfall. It’s because the pure state of the land has been altered by settlement, roads, deforestation, livestock grazing and cultivation. In consequence, a better proportion of rainfall runs off. This runoff is extra fast and erosive, and fewer water infiltrates to replenish groundwater shops.
The East African Flood Mannequin, a regular drainage design software, demonstrates that by lowering a forested catchment right into a subject for livestock pasture, as an illustration, the height flood magnitude can enhance 20-fold. This type of catchment degradation results in landslides, dams can breach, and street culverts and irrigation intakes are recurrently washed away.
Land degradation in sub-Saharan rangelands is omnipresent, with over 90% rangeland degradation reported in Kenya’s northern drylands. Kenyan analysis has recorded dramatic will increase in stormwater runoff as a result of overgrazing.
Second, human stress in city areas – together with encroachment into riparian zones and lack of pure flood storage buffers by the destruction of wetlands – has elevated flood dangers. Riparian zones are areas bordering rivers and different our bodies of water.
By 2050, half of Kenya’s inhabitants will stay in city areas. Inexperienced house is progressively being crammed with buildings and pavements. A big proportion of city inhabitants lives in tin-roofed slums and casual settlements missing sufficient drainage infrastructure. In consequence, nearly the entire storm rainfall is translated into fast and typically catastrophic flooding.
Third, flood dangers are worse for individuals who have settled in vacant land which is usually in low-lying areas and inside flood plains. In these areas, inundation by flood waters is inevitable.
Fourth, Nairobi’s persistent water provide shortages have led to a proliferation of boreholes whose over-abstraction has resulted in a dramatic decline within the underground water desk’s ranges. This results in aquifer compression, which is compounded by the burden of buildings. The result’s floor degree subsidence, which creates low spots the place stormwater floods acquire.
What ought to be finished to minimise the dangers?
Rural areas require a distinct set of options.
Pure watercourses all through Kenya are being scoured out by bigger floods as a result of land use pressures. These watercourses are increasing and riparian vegetation cowl is disappearing. The flood plains want house to regenerate the pure vegetation cowl as this attenuates floods, lowering the pressure of runoff and erosion.
There are present legal guidelines to guard riverbanks, and livestock actions in these areas should even be managed. Any constructing or casual settlement inside riparian areas is illegitimate and would in any other case be uncovered to the risks of floods. Enforcement is a problem, nonetheless, as these areas are favoured by human actions and infrequently these persons are among the many poorest.
City areas have a number of explicit challenges that must be addressed.
Take Nairobi, Kenya’s capital metropolis. The bodily planning course of is hindered by corruption. Inappropriate and unsafe developments proliferate alongside insufficient water provide, wastewater and stable waste disposal infrastructure. Sewage effluent is usually discharged into stormwater drains, even in high-class areas of the town. And there’s little management of growth within the rising city centres bordering Nairobi, with transport corridors being congested. All through the nation, legal guidelines that shield riparian zones are flouted.
None of that is sustainable.
Every municipality is obliged to supply infrastructure that features an efficient engineered stormwater drainage community. And in parallel, wastewater and stable wastes should be individually managed.
The everyday stormwater drainage community contains adequately sized earth and lined channels, and pipes and culverts that convey the stormwater to the closest watercourse. Fixed upkeep is crucial, particularly earlier than the onset of rains, to keep away from blockage by rubbish and different human actions.
Fashionable-day city flood mitigation measures embrace the supply of flood storage basins. Sadly that is not possible in Nairobi the place developments are constructed proper as much as the sting of watercourses. Constrained channels thereby trigger upstream flooding as there’s nowhere else for the water to go.
Makes an attempt have been made to reverse city riparian zone encroachments, however these efforts faltered as a result of authorized repercussions. To at the present time, unscrupulous builders encroach with impunity.
It’s important that the authorities demarcate riparian boundaries and put aside buffer zones that can not be “developed”.
