When a Forecast Becomes an Address

The new Nairobi assessment is useful precisely because it separates scenarios. The medium case is 22,000–25,000 households. The upper figure of 100,000 households is a worst case. Treating the larger number as inevitable would turn risk assessment into alarmism.

But even the medium scenario would represent a substantial urban emergency. And the 246 mapped hotspots show that the danger is not confined to one riverbank or one densely populated low-income neighbourhood. Flooding can disrupt roads, commercial areas, transport, sanitation, schools and health services across the city.

For the households most exposed, however, the meaning is more immediate. A weather warning is not only information about rain. It can become a decision about whether to leave a home, where to sleep, how to protect possessions, whether work can continue and whether returning afterwards will be possible.

For many Nairobi residents, the coming rains are frightening not because they do not know what flooding can do. They are frightening because they do.

A July 2026 World Resources Institute study of flooding in Nairobi’s densely populated low-income settlements found that the March–May 2024 floods displaced 20,968 families. The study describes damage to roads, bridges, homes, schools, sanitation systems, transport and livelihoods, with Mathare, Mukuru and Kibera among the areas hit particularly hard.

The World Resources Institute (WRI) argues that Nairobi’s flood risk is produced by an interaction: extreme rainfall meets settlement in floodplains and riparian corridors, inadequate drainage, blocked waterways, degraded wetlands and green spaces, weak land-use enforcement and fragmented disaster-risk governance.

That distinction matters. Rain is the trigger. It is not the whole explanation for the disaster.

The government’s response to the 2024 floods also shapes how new warnings are heard. In May 2024, national authorities ordered people living within a 30-metre riparian corridor along rivers and other watercourses to leave, with mandatory evacuation and removal of structures threatened for those who remained.

Civil-society organisations including Amnesty International Kenya warned at the time that the measures could permanently displace more than 127,000 Nairobi residents and criticised the absence, at the point the orders were announced, of a viable relocation action plan, completed enumeration and clear compensation arrangements.

The government subsequently offered KSh10,000 relocation support to affected households and promised priority within the Affordable Housing Programme. The emergency rationale was clear: people should not remain in places where rising water could kill them. The human dilemma was equally clear: leaving a dangerous home is much easier when another safe and affordable home exists.

Amnesty International Kenya later reported that more than 6,000 households were demolished during forced evictions associated with the 2024 flooding and called for compliance with court-ordered compensation in several affected communities.

This is why evacuation cannot be treated as a purely behavioural question. A household may understand a warning perfectly and still have very few workable choices.

Affordable housing is therefore directly relevant to flood resilience. Safe, secure and affordable alternatives can reduce the pressure that pushes low-income households towards riverbanks, drainage corridors and other high-risk land.

The scale of the government’s ambition is large. President William Ruto said in 2022 that the goal was 250,000 new houses a year for low-income earners. The State Department for Housing and Urban Development reported at the end of August 2026 that 10,107 units had been completed since September 2022, while 196,846 units were under construction. Other categories, including institutional and student accommodation, take the combined completed-and-ongoing figure higher.

The government also says tens of thousands of additional units are approaching completion and has set a target of making 45,000 units available by the end of 2026. The programme is real, construction is visible and the pipeline is substantial.

But preparedness works on a different clock. A house under construction cannot shelter a family from a flood arriving this year.

Nor is supply the only question. Housing must be affordable and accessible to the people being asked to leave high-risk areas. A long-term programme can be part of the solution without yet being an immediate answer for a household deciding what to do when an evacuation message arrives.

The World Resources Institute describes flood risk through three interacting ideas: hazard, exposure and vulnerability. Heavy rainfall is the hazard. Living or working where water is likely to accumulate creates exposure. Vulnerability determines how much damage that exposure produces and how difficult recovery becomes.

Two households can experience the same storm and face radically different consequences. One may have savings, insurance, secure tenure, a vehicle, paid leave and relatives with a spare room. Another may depend on daily income, live in a single-room structure beside a river, have nowhere nearby to move belongings and risk losing both shelter and livelihood by leaving.

That is why early warning, although essential, cannot carry the whole burden of preparedness. A warning does not create transport. It does not create a safe destination. It does not replace lost income. It does not guarantee that a household can return.

In densely populated low-income neighbourhoods, the practical question can therefore be brutally simple: what can people do if they are told to move but are given too little help to make moving possible? That is not necessarily fatalism. It can be a description of constrained choices.

The current response is not simply a repetition of 2024. Nairobi County says it has begun clearing and deepening drainage channels, removing silt and waste, opening waterways and coordinating emergency response across agencies.

Governor Johnson Sakaja has described a KSh2.4 billion multi-agency flood-resilience programme involving Nairobi County, the Kenya Red Cross, the Kenya Urban Roads Authority (KURA) and the Kenya National Highways Authority (KeNHA). The structure includes committees for infrastructure and drainage, evacuation, shelter and relief, security and traffic, and public communication.

The county also says rescue teams, boats, emergency lines and relief support will be available, while schools and other sites have been identified as possible temporary holding areas. The health sector is preparing for water- and food-borne diseases including cholera, typhoid, dysentery, hepatitis A and diarrhoeal illness.

These measures matter. Clearing a blocked drain before a storm can prevent damage. A functioning warning system can save lives. A prepared rescue team can change an outcome.

The question is not whether Nairobi is preparing. It is whether the scale and timing of preparation match the scale of the vulnerability already mapped.

The World Resources Institute’s 2026 assessment is particularly useful because it resists a simple climate explanation. Nairobi’s geography makes flooding possible, but urban decisions help determine its severity.

Development in floodplains and riparian areas increases exposure. Impervious surfaces accelerate runoff. Degraded wetlands remove natural storage. Inadequate drainage and solid-waste blockages prevent water from moving safely. Weak enforcement allows dangerous land use to persist. Fragmented responsibility makes prevention harder to coordinate.

None of this means residents of high-risk areas simply chose badly. For many low-income households, proximity to work, rent levels and the scarcity of affordable alternatives constrain where they can live. Removing a structure without changing those underlying conditions can relocate vulnerability rather than eliminate it.

That is why the strongest flood policy is not merely faster emergency response. It is a city in which fewer households need emergency rescue in the first place.

The 100,000-household figure will attract attention because it is large. It should. But the more useful number may be 22,000–25,000: the medium scenario that planners currently expect to manage if the coming rains produce serious flooding.

Either way, Nairobi has been given something valuable before the water rises: time.

The city knows many of the places where flooding repeatedly occurs. It knows that drainage and waste management matter. It knows that households beside rivers face greater danger. It knows that evacuation without viable relocation can become another crisis. And it knows, after 2024, how expensive delayed action can be.

Preparedness should therefore be judged twice. First by what government and Nairobi County do before the rain: drainage, warnings, shelters, rescue capacity, relocation planning and protection of public health. Then by what happens afterwards: whether displaced families receive meaningful support, whether temporary evacuation becomes prolonged homelessness, whether promised housing becomes accessible housing and whether the same hotspots remain equally dangerous when the next forecast arrives.

A forecast tells Nairobi what may fall from the sky. The real test is what the city and the state have changed on the ground.

For European readers, Nairobi’s flood risk is a useful correction to the way climate disasters are often described. Extreme weather matters, but damage is never produced by weather alone.

The same principle applies in European cities: infrastructure, housing, planning, insurance, emergency services and household wealth shape who can absorb a shock. Nairobi makes those inequalities unusually visible because rapid urban growth, housing shortages and infrastructure gaps place very different levels of protection within the same city.

Climate adaptation funding therefore cannot be reduced to forecasts and emergency equipment. It also concerns drainage, housing, land use, public health, community participation and institutions capable of acting before the crisis. Development partners that finance climate resilience should ask not only how many warnings were issued, but how many households were actually able to act on them.

Rainfall forecast: how the Kenya Meteorological Service Authority updates the October–December outlook and whether Nairobi’s expected rainfall intensifies or weakens.

The 246 hotspots: whether Nairobi County publishes a detailed, accessible map and clarifies how the latest list relates to earlier mappings.

Medium versus worst case: whether planning remains centred on the 22,000–25,000 household scenario while retaining capacity for a much larger emergency.

Shelter and evacuation: where temporary holding centres will operate, how long people can remain there and what support is available to households unable to return safely.

Drainage works: whether the KSh2.4 billion resilience programme produces visible improvements in repeatedly flooded corridors before the short rains peak.

Housing: whether units promised under the Affordable Housing Programme become accessible to households displaced from high-risk areas, rather than remaining a long-term policy promise disconnected from immediate relocation needs.

After the flood: if severe flooding occurs, watch not only fatalities and rescues but displacement, compensation, return, rebuilding and whether families are left safer than before.