MODELLING THE EFFECTS OF URBAN MORPHOLOGY ON ENVIRONMENTAL QUALITY OF NAIROBI CITY, KENYA

Abstract

Various postulations have been put on the correlation between urban morphology and the urban environmental quality (UEQ). However, the studies have not quantitatively demonstrated the contributions of each morphological parameter in the determination of the UEQ. It is this gap in knowledge that this study sought to fill by modelling the relationship existing between the urban morphological variables of development density, land uses and vegetation density and the UEQ parameters of the surface temperatures and the air quality values of Nairobi City. The specific objectives of the study were to evaluate the impact of land use and land cover changes on the Land Consumption Rate and Land Absorption Coefficient for Nairobi City between the years 1988 to 2015, to determine the relationship existing between the urban morphology of Nairobi City and the surface temperature values using geospatial techniques, to establish the relationship existing between the urban morphology of Nairobi City and the variations in air quality, to establish a spatial and quantitative model depicting and explaining environmental quality variations in the city as well as to propose strategies for the achievement of sustainable environmental quality for the city. The study adopted both descriptive and quantitative research design. All the 30 development zones of the city as detailed out by the Nairobi City County Government constituted the target population. This study was aided by Digital Image Processing of Landsat 5 TM imageries of the years 1988 and 1995, Landsat ETM+ imageries of the years 2000, 2005, 2010 and 2015 as well as the IKONOS satellite imagery of the city for the year 2015. Together with the topographical and development zoning maps of the city, other secondary information such as the census reports for the city covering years under consideration were also utilised. Establishment of the air quality values involved in-situ viii measurements of the concentration of carbon dioxide, nitrogen dioxide, sulphur dioxide and suspended particulate matter. The Landsat imageries were further used in analysing the distribution of the surface temperatures within the city. The environmental implications of the above stated parameters were transformed into numerical values ranging from 1 to 10 of which lower values (1) were accorded to development zones whose morphological, thermal and air quality attributes have higher negative impacts on the city’s environmental quality and vice-versa. The aggregate values for the development zones were arrived at through aggregation of the numerical values assigned to the parameters within a development zone. The above was superimposed with development zoning boundaries and converted into a spatial model depicting environmental quality variations within the city. Bivariate and multivariate statistical models of Pearson’s correlation coefficients (r), coefficients of determination (R), t-tests and the Analysis of Variance (F-tests) with levels of significance decided at 95% were also used to determine the strengths, significances and consistencies of the relationships existing between and among the study variables. The study established that while urban built-up, open/transitional areas and forest covers within the city increased during the study period, rangelands, agricultural, grass, secondary growth and riparian vegetations declined. The study confirms that vegetation density is the most significant morphological variable influencing the distribution of the UEQ. This is followed by the development density and land uses in the order of significance. However, the significance of the error term in the model representing the relationship existing between the UEQ and the urban morphological variables implies that other factors such as topography, pedology, rainfall pattern and amount, slope, aspects and wind velocity which were not considered by the study are equally significant in determining the distribution of the same.