Estimating urban greenness index in the city of Johannesburg: a case study of Soweto vs Rosebank suburbs
Date
2019
Authors
Mudede, Marko Freddy
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Abstract
Urban greenness plays a significant role in providing ecosystem services and disservices which directly affects the health status of urban city's dwellers. Factors like impervious concrete surfaces or tarred roads and tree cover contribute to changes in urban land surface temperature. The change in urban temperatures will result in differing local temperatures compared to surrounding areas leading to urban heat island effect. Urban greenness index in the city of Johannesburg of South Africa was investigated in Soweto and Rosebank suburbs to determine its environmental suitability for its inhabitants. A total of 120 street tree species composed of Jacaranda mimosifolia and Platanus acerifolia were recorded, and GPS points from each of these trees were collected from Rosebank for ground-truthing. In this study two satellite images of Landsat 8 and SPOT 6 were used for analysis. Landsat 8 data was used to evaluate the effects of urban heat island phenomenon based on urban thermal field variance and ultraviolet indices. Soweto had the highest total biomass of 504399.97 tons while that of Rosebank was 113179.03 tons. However, Rosebank suburb had a higher greenness index value of 0.82 compared to that of Soweto (0.14) and this gives a clear pattern of the ecological disparity between the two areas. The Land Surface Temperature (LST) of Soweto showed a higher value (2.58 oC more) compared to that of Rosebank suggesting that high-density areas are hotter than low-density suburbs. Pearson correlation coefficient was performed among NDVI, LST and Normalized Difference Built-up Index (NDBI) and a confusion matrix were derived. The results showed a positive correlation between LST and NDBI (0.92 and 0.98) and a negative correlation between LST and NDVI (-0.91 and -0.99) and NDVI vs. NBDI (-0.90 and -0.85) in Rosebank and Soweto areas. Based on urban thermal field variance (UTFVI) analysis, it shows that residents of Soweto face more thermal discomfort compared to residents of Rosebank suburb. Similarly, analysis of the global solar ultraviolet index (UVI) indicated that Soweto residents’ life is more vulnerable to prolonged exposure to ultraviolet solar radiation than those in Rosebank. Overall, land surface temperature for the two study areas was successfully retrieved from Landsat 8 data and the information obtained from this study will provide a baseline for future planning on improving the greenness of urban cities
Description
A research report submitted in partial fulfillment of the requirements for the degree of Master of Science
University of the Witwatersrand
School of Animal, Plant and Environmental Sciences
May 2019