Abstract
Nairobi city in Kenya is an example of the many cities in Africa experiencing rapid growth and too many environmental impacts, including the urban heat islands (UHI) phenomenon. UHI develops and escalates under outrageous hot periods, such as during heatwave, which can affect outdoor microclimate, human thermal comfort, and health and also increase the energy demand for cooling. This study used the MUKLIMO_3 model to reveal the spatial heterogeneity and temporal variability of 2 m air temperature fields and thermally sensitive areas within Nairobi city. The model reproduced the potential summer day conditions through idealized simulations of temperature, wind, and relative humidity based on the urban topography and local climate zones (LCZs) data at a spatial resolution of 200 m. The aim was to expand knowledge of urban climate change based on the accompanying extensive modification of land use and land cover that are critical for the local-scale atmospheric circulation. The model results revealed intricate spatiotemporal patterns of 2 m air temperature fields, which accrued from terrain-induced flows and land surface heterogeneity as described by the LCZ parameters. The variation in canopy layer UHI was a joined impact of the unfavorable location of the town and urbanization process, which added to the formation of excessive urban heat load. The study concluded that the enhancement of urban heat load in Nairobi city could be linked to the concept of rapid urbanization process and its historical development. Therefore urban planning strategies such as optimization of mixed building heights and the introduction of green & blue infrastructure were critical to mitigating heat-stress across Nairobi city.
Highlights
Urban climate change is a severe problem for cities around the world (Hashim & Hashim, 2016), in developing countries like Kenya, where urbanization is happening at a fast rate (Alavipanah, Wegmann et al, 2015)
The study concluded that the enhancement of urban heat load in Nairobi city could be linked to the concept of rapid urbanization process and its historical development
The results indicated a complex spatial structure of the simulated 2 m air temperature and urban heat load in Nairobi City
Summary
Urban climate change is a severe problem for cities around the world (Hashim & Hashim, 2016), in developing countries like Kenya, where urbanization is happening at a fast rate (Alavipanah, Wegmann et al, 2015). Urbanization prompts changes in the landscape (Oyugi, Odenyo, & Karanja, 2017), as infrastructure replace vegetation and open land making the surfaces that were once porous and sodden to end up impermeable and dry (Ali, Patnaik, & Madguni, 2017; Hashim & Hashim, 2016; Middel et al, 2014; Ren et al, 2016; See et al, 2015; Singh, Kikon, & Verma, 2017) Tropical cities such as Akure in Nigeria, Cairo in Egypt, and Nairobi city in Kenya are currently experiencing heat waves, and they are expected to face further the challenge of increased intensity, duration, and spatial distribution of heat waves (Connor et al, 2015). Its (UHI) fundamental drivers are believed to identify with the three attributes of urban areas: increased roughness due to building structural geometries, drier and progressively impenetrable surfaces and anthropogenic warmth and moisture discharges (Bechtel et al, 2015; Bechtel & Daneke, 2012; Geletič et al, 2018; Stevan et al, 2013)
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