El Nino is a natural climate pattern that begins thousands of kilometres away in the Pacific Ocean but can significantly influence weather in countries such as Kenya.
As Kenya prepares for the October-December rainfall season, experts are urging communities and authorities to prepare for the hazards that can accompany heavier rains.
Disaster risk management expert Zachary Misiani, speaking on Spice FM on Wednesday, September 16, explained that El Nino occurs when sea surface temperatures in the central and eastern equatorial Pacific become unusually warm. The warming alters winds, atmospheric pressure and circulation, affecting rainfall patterns far beyond the Pacific.
The World Meteorological Organisation defines El Nino as the warm phase of the El Nino-Southern Oscillation, or ENSO. Its effects vary by region and from one event to another.
In Kenya, El Nino is often associated with above-normal rainfall, particularly during the October-December short rains.
The Kenya Meteorological Department has forecast above-normal rainfall across much of the country during the season.
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Misiani said the focus should now be on preparedness, noting that the impact of heavy rain depends not only on how much falls, but also on how exposed and prepared communities are. “El Niño is going to happen,” she said, stressing the need for early action rather than waiting for disasters to occur.
From drought to floods
Kenya experienced prolonged La Nina conditions from 2020 to early 2023, contributing to poor rainfall and severe drought in parts of the country.
La Nina is the cooler phase of ENSO and can produce weather patterns broadly opposite to those associated with El Niño.
The drought was followed by the strong 2023-24 El Nino, which brought heavy rainfall and flooding to parts of East Africa.
Kenya's position around the Equator also influences its rainfall patterns. Moist air rises as winds converge around the Equatorial region, causing water vapour to condense and form clouds. Changes in large-scale atmospheric circulation during El Niño can alter the amount, timing and distribution of rainfall.
But heavy rain does not automatically result in disaster. “The problem is not the rainfall but how prepared we are,” Misiani said.
What are the risks?
Heavy rainfall can trigger riverine and flash floods, urban flooding, lake backflow, thunderstorms, lightning, strong winds, large ocean waves and dam overflows.
Riverine flooding occurs when rivers receive more water than their channels can carry, forcing them over their banks. Vulnerable areas include parts of Tana River and Garissa counties in the Lower Tana Basin, as well as Kisumu, Busia, Siaya, Homa Bay and Migori in the Lake Victoria Basin.
Flash floods can develop within minutes or hours of intense rainfall, particularly in areas with poor drainage or steep terrain.
Urban flooding is also a concern when drainage systems are overwhelmed. Nairobi, Mombasa, Narok and Kisumu are among the areas that need to remain alert.
Rising lake levels can restrict the normal flow of rivers and drainage systems, leaving water trapped in surrounding low-lying areas. Communities around Lake Victoria, particularly in Kisumu, Homa Bay and Busia, are vulnerable. Rising water levels in Rift Valley lakes, including Naivasha, Nakuru, Baringo and Bogoria, also require monitoring.
Thunderstorms and lightning can threaten people, livestock and infrastructure, while strong winds can damage buildings and trees. At the coast, large waves can endanger communities and marine activities.
Dam overflows can also increase downstream flooding when reservoirs receive large volumes of water over a short period.
Preparing before the rains
The disaster risk management expert averred that preparedness should involve national and county governments, communities, humanitarian agencies and other stakeholders.
Authorities should identify people living in high-risk areas and, where necessary, move them to safer ground before flooding occurs. Preparedness should also cover health, education, roads and transport.
Early warning information must reach communities in time to act, Misiani said. He added: “Everyone should have access to early warning information and it should be translated into different languages.”
He called for the use of media, National Government Administration Officers, text messages and other communication channels to ensure warnings reach the public.
El Nino cannot be stopped, but its risks can be reduced through early warnings, better planning, stronger drainage and infrastructure, protection of vulnerable communities and coordinated emergency response.