An investigation of urban heat island phenomenon in Nairobi
Amboga, Reginald M
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The Urban Heat Island phenomenon is a widely documented subject of inadvertent climate modification associated with the rapid development and growth of urban settlements in the 21st century. Whereas the phenomenon is well defined for temperate cities, it is not very clear for cities in the tropics. This study sought to establish if the urban heat island phenomenon is well defined in Nairobi city, its characteristics, intensity, spread and environmental impact. Objectives of the study included determining the occurrence of the Urban Heat Island over Nairobi, the characteristics of Urban Heat Island and the Urban Heat Island impact on the environment in Nairobi. The study used the hypothesis that the Urban Heat Island does not exist over Nairobi city and therefore is of no consequence in urban air quality. The study considered the nocturnal heat island using minimum temperature records collected over a period of twenty years between 1991-2011. Minimum temperature of the day was used for the study because the Urban Heat Island tends to be most pronounced in the hours between sunset to sunrise. Purposive sampling was used for data collection. The resulting synoptic data were subjected to descriptive analyses, time series analyses, a control plot analyses and Kruskal-Wallis H-test analysis. The significance of the results were tested, if necessary, at alpha 0.05. The wind rose technique was used to give an indication of the heat island plume. Impact was assessed using analysis of surface level (above 600mb) ozone concentrations. Ozone data was analyzed using profiles developed from ozonesonde data. The study concluded that the Nairobi heat island does exist though not clearly defined; its characteristics vary with seasonal changes and its impact on the Nairobi environment could not be fully established however impacts of the heat island warrant further studies.