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Nairobi concrete jungle turning city into oven

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Nairobi City skyline. FILE PHOTO | NMG

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Summary

  • Data over Nairobi indicates that average air temperatures increased from 18.8° Celsius (C) in the 1950s to 19.5°C in 2000s.
  • Kenyan scientists Victor Ongoma and Patricia Mwangi observe Nairobi’s heat-island phenomenon will likely become dire given the ongoing environmental modification through construction.
  • Being one of the fastest growing cities in the continent, Nairobi’s population, which was about 2 million people a decade ago, now stands at over 4 million, putting intense pressure on the natural environment.

Whichever side of Nairobi you are living in, you must have realised nights in the city have become outrageously warm over the recent months that you rarely can afford a comfortable sleep.

Also mosquitos are quickly surging in numbers, not forgetting some few years ago you could hardly sight any.

Well, scientists link the ballooning numbers of the parasitic insects to the city’s rising temperatures. Basically as concretes take over the city, clearing way for buildings, metals, tarmacs and all none-green infrastructures, a lot of sun’s energy is absorbed by these impervious surfaces which they later release back into the atmosphere at night.

Owing to this phenomenon which scientists call urban heat-island effect, cities tend to be unbearably warmer, than rural areas surrounding them.

Data over Nairobi indicates that average air temperatures increased from 18.8° Celsius (C) in the 1950s to 19.5°C in 2000s.

Kenyan scientists Victor Ongoma and Patricia Mwangi observe Nairobi’s heat-island phenomenon will likely become dire given the ongoing environmental modification through construction.

Being one of the fastest growing cities in the continent, Nairobi’s population, which was about 2 million people a decade ago, now stands at over 4 million, putting intense pressure on the natural environment, says Ms Mwangi, a geospatial engineer and urban planner.

Even so, researchers warn that climate change could exacerbate urban heat-island effect across the world to levels never seen before.

Using a new modelling technique, an international team of researchers observed that world’s cities could averagely warm by as much as 4.4°C by 2100.

In a new study published last week in the Nature Climate Change, Prof Lei Zhao and his team notes that hotter cities could be catastrophic for urban public health, which is already suffering from the effects of increasing heat.

CLOSING THE GAP

Until recently, there weren’t any global climate models for urban areas as researchers snubbed them — since they make up just three percent of the planet’s land surface — to focus on more major issues such as the ocean, ice, and air currents.

“We're closing this kind of gap,” says Prof Zhao, a climate scientist and the papers lead author, “We provide urban-specific projections for the future.”

World Health Organisation (WHO) estimates that the number of people exposed to heat waves jumped by 125 million between 2000 and 2016, while extreme heat claimed more than 166,000 lives between 1998 and 2017.

And while at the moment half the world’s population lives in urban areas, that proportion is expected to rise to 70 percent by 2050, according to the new paper authored by Prof Zhao.

Dr Ongoma, a meteorologist and a climate change expert, notes that at certain times of the year, parts of Nairobi experience temperature spikes of up to 4.8°C and are associated with increases in mortality, especially in children and the elderly.

Although the intensity of Nairobi’s heat-island is yet to hit alarming levels of directly causing deaths, Dr Ongoma cautions the ongoing developments could eventually result in major disasters.

He says residents of large slums – such as Kibera, Mathare and Mukuru – are more vulnerable due to population density and housing infrastructure that is characterised by poor ventilation.

The researchers warn that urban heat-island will worsen conditions such as respiratory issues and heart diseases caused by household air pollution in these settlements.

In a bid to ease heat distress, household many turn to electric fans and air conditioners for cooling, further resulting in increased consumption of electricity.

“The increase in demand and consumption of electricity has financial implications at a household level and increases carbon footprint in the atmosphere,” Dr Ongoma notes.

Besides causing thermal discomfort, heat and humidity can be dangerous; resulting even in deaths, writes Prof Camilo Mora who authored a researcher paper on 27 ways heat can kill a person.

When your body detects that it is overheating, it redirects blood from the organs at your core to your skin, thus dissipating more heat into the air around you. (This is why your skin turns red when you’re hot.) In extreme heat, this can spiral out of control, resulting in ischemia, or critically low flow of blood to the organs.

This can damage crucial organs like the brain or heart. In addition, a high body temperature can cause cell death, known as heat cytotoxity. Humidity compounds the risk of overheating and organ failure, since one can’t sweat as efficiently to cool down.

Extreme heat can harm healthy people, and those with heart or respiratory conditions like asthma are particularly vulnerable. Children are also at particular risk because of the thermodynamics of their bodies; their small size means that they both heat up and cool down faster.

Researchers suggest that building green infrastructure and increasing urban vegetation might be a safe bet for cities looking to mitigate rising temperatures.

Trees and vegetation help to reduce temperature by releasing water into the atmosphere, which cools down the air. This has been seen as having a limited effect in places which are already humid, but Prof Zhao’s new model predicts that air in most non-coastal cities will become drier in the next century.

According to an article published in American magazine WIRED, each tree’s leaves also act like tiny air conditioners, releasing moisture to cool the environment. And the less the pavement is exposed to the sun, the less the built environment will absorb its energy.

The suggestion would no doubt contribute immensely in tackling rising temperatures in Nairobi which has estimatedly lost 22 percent of its green space covers between 1988 and 2016.

To calculate how much city temperatures might rise, Prof Zhao and his colleagues built a statistical model for the climate of urban regions, focusing on changing temperatures and humidities.

These two factors are the conspiring menaces of extreme heat: Our bodies respond to high temperatures by perspiring, which is more fancily known as evaporative cooling. But humidity makes this process less efficient, because the more moist the air is, the less readily it accepts evaporating sweat from our bodies. That’s why humid heat feels so much more uncomfortable than dry heat.

URBAN PLANNING

Prof Zhao hopes the data will allow urban planners and policymakers to make more informed decisions about mitigating rising temperatures in their cities.

“Some strategy might work for a city, but not necessarily for your city,” he said. “When you look at large-scale projections, you can see if the warming signal is different from other places, and how humidity levels vary, so it can help you form the strategy differently.”