Influence of Urban Form on Climate Vulnerability in the City County of Nairobi

Abstract

Urban form has the potential to influence urban climate. This in turn affects climate vulnerability. Urbanization characteristics pertinent to this relationship include imperviousness, reduced concentration of vegetation, increased density of built-up areas, and a socio-economically vulnerable population. The City County of Nairobi is rapidly urbanizing more reactive than through anticipatory physical planning regime. Together with the city’s unique biophysical and socioeconomic dynamics, Nairobi has remained susceptible to climate related hazards. The objectives of the study included examining the evolution of Nairobi’s urban form, the climatic trends and patterns, and the relationship between urban form and climate. The study hypothesized that urban form significantly influences climate vulnerability. The survey used a descriptive case study design for the period between 1988 and 2018. The main variables were urban form, socioeconomic characteristics, and climate. The elements of urban form were landcover, soil, elevation, slope, and Normalized Difference Vegetation Index. The parameters of climate were average annual maximum, average annual minimum, highest annual and lowest annual temperatures, and rainfall. With the unit of analysis as sublocations, data were collected using observation checklists, self-administered questionnaires, and archival review. Data analysis methods included cross-tabulation, change detection analysis, time-series analysis, correlation, and regression. Hypothesis was tested at 95% confidence interval. The findings revealed an evolving urban form and changing climatic patterns. Urban form evolution manifested as 147% increase in built-up areas, 46% reduction in vegetation cover, and a 21% reduction in the Normalized Difference Vegetation Index. With the current trends held constant, 2048 projections revealed 21% reduction in open space, 60% reduction in Normalized Difference Vegetation Index and 44% increase in Built-Up Area. Climatic trends and patterns showed a 1.5℃ rise in average annual minimum and lowest annual temperatures between 1988 and 2018 with 5% - 14% increase in the minimum and extreme temperature values for the year 2048. The correlation and regression analyses showed, in descending order, Normalized Difference Vegetation Index, Forest and Built-Up Area as the influencers of climate. These relationships led to varying levels of flooding and thermal stress vulnerability at the sublocation level. Ninety five percent of the sublocations showed moderate to very high thermal stress vulnerability while only 13% showed low vulnerability to flooding. The study findings strongly by supported the Integrated Urban Ecosystems Theory and advocated for the triangulation research approach in climate vulnerability assessment studies. It recommended an overall strategy of ecosystem-based urban planning and development to take advantage of ecosystem services offered by the green urban systems. These would be realized through distributive open space planning, green and blue system planning.