Nairobi buildings cause heat waves — study

Green space, tree canopies, vegetation, water, help cool, reduce heat island effect

In Summary

• Although it's a mile above the Equator, Nairobi's surface temperature is rising and massive infrastructure projects contribute to heat island effect 

•In the past year, booming infrastructural developments replaced trees, many of them old and providing canopies. 

Motorists driving on expressway, Saturday, May 14.
HEAT ISLAND Motorists driving on expressway, Saturday, May 14.

Heat waves in the city of Nairobi have been linked to more buildings, more concrete reflecting heat.

And to less greenery, trees and tree canopies providing shade and cooling less greenery, fewer trees and tree canopies providing cooling and shade.

The study by Dr Francis Oloo of the Technical University of Kenya showed that climate-related changes have contributed to heat waves around cities in what is called the heat island effect.

Urban heat islands occur when cities replace natural land cover with dense concentrations of pavement, buildings and other surfaces that absorb and retain heat.

This increases energy costs for air conditioning, air pollution levels and heat-related illness and mortality.

Oloo’s study mathematically estimated land service temperature using Landsat 8 data for the city of Nairobi between 2013 and 2021.

Landsat 8 is an American earth observation satellite launched 2013. It is a collaboration between Nasa and the US Geological Survey.

He assessed ward-level patterns of land surface temperatures, how hot the surface of the earth feels to the touch in a particular location.

“The net effect of the rise in temperature in cities is a degradation of the quality of life (discomfort), the emergence of various diseases and increased energy expenditure,” he said in his study.

Dr Oloo is an expert in geo-informatics with experience in spatial simulation modelling, spatial analysis of renewable energy potential, land degradation mapping.

Also land health monitoring, satellite image processing and interpretation, web mapping and spatial analysis of epidemiology.

The study was presented last week during the international conference on earth observation technologies at the Regional Centre for Mapping of Resources for Development in Nairobi.

The conference was themed 'Earth observation services for resilient social systems'.

Dr Oloo said human settlements emit carbon dioxide, increasing urban heat.

Booming infrastructure developments have been taking place in Kenya's capital city to the detriment of trees. The state seeks to decongest roads notorious for traffic jams.

The major ongoing project, the Nairobi Expressway (JKIA James Gichuru Expressway) required felling about 500 trees to make way for the four-lane and six-lane dual carriageway.

It runs within the existing median of Mombasa Road-Uhuru Highway-Waiyaki Way.

The trees are yet to be replaced.

Trees have also been cleared elsewhere within the city to accommodate more infrastructure.

Moreover, Dr Oloo said air conditioning releases heat into the atmosphere.

(Edited by V. Graham)

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