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City rains not normal, local experts admit

Weather experts on Friday acknowledged that the rains that have pounded Nairobi and other parts of the country this month were unusually heavy.

The rains also varied in different parts of the city.

“Our station here in Dagoretti Corner recorded up to 189mm for the two days. That’s very, very heavy because it’s even more than the long-term average for the whole month of May,” said Mr Samuel Mwangi, the deputy director of the Kenya Meteorological Department on Thursday.

For two consecutive nights early this week, the rains pounded Nairobi.

The ensuing floodwaters killed ten people, rendered homes uninhabitable, submerged vehicles and kept vexed, exhausted commuters on the road until the wee hours.


A group of city school children were trapped in their bus for over six hours.

But Mr Mwangi explained that these were normal long rains not caused by El Nino.

“We can’t say this has anything to do with the global phenomenon, because indeed El Nino has very little relationship with the long rains in Eastern Africa and Kenya for that matter.”

In East Africa, El Nino rains are witnessed from November to December.

Mr Mwangi made the remarks a day before a US advisory placed chances of El Nino continuing to the end of 2015 at greater than 80 per cent.

Australian scientists were also predicting a strong event. “This will be quite a substantial event. It’s not a weak one or a near miss,” Mr David Jones, head of climate monitoring at Australia’s Bureau of Meteorology told the Sydney Morning Herald.

El Nino is caused when waters in the eastern Pacific Ocean off the coast of Peru get warm, leading to changes in weather patterns around the world.


In East Africa, it causes downpours during the October to December short rain period, with little influence on the long rains that occur from March to May.

However, Professor Nzioka Muthama, an expert in meteorology at the University of Nairobi, stressed that the onset of El Nino in the Pacific Ocean does not necessarily result in increased rainfall for East Africa.

He explained that El Nino goes through the onset, growth and maturity stages.


“The El Nino may set on but not grow, or decay before it matures,” he said.  If El Nino’s effects were felt in Kenya, not every town would necessarily receive high rainfall, he said.

He cautioned that due to many uncertainties, it was impossible to confidently predict what would happen six months in advance, although a clear rainfall prediction for Kenya was possible from around August.

Mr Mwangi said it was impossible to isolate a particular cause of events like the recent floods, noting that urban development played a role.

For example, cities are more susceptible to storms than less built up areas, due to what he described as an urban heat island.

“These buildings not only generate heat, but also capture solar radiation, such that in a built up area, the temperatures are slightly higher than the surroundings.

“When this interacts with the atmospheric variables, humidity and so on, it can sometimes enhance convection, and sometimes you see that urban areas tend to experience some severe storms”.

He added that the paving in cities also made flooding more likely.  “In the urban areas there is a lot of pavement, tarmac, and buildings. All these prevent water from seeping into the ground and therefore tends to collect a lot on the surface,” Mr Mwangi added.

Source: Daily Nation