Impact of urban development on climate and river systems: implications for the environmental health sustainability of the Mangaung metropolis, South Africa.

Abstract

The emigration to urban areas puts pressure on available resources, thereby increasing the scarcity of natural resources and changes in lifestyles. The overpopulation of urban centres accelerates land use patterns, slum creation and generation of contaminants. Urban centres are known to generate carbon dioxide and other compounds that increase greenhouse gases. In the process of combating food insecurity, farmers resort to chemicals such as fertilisers, pesticides and fungicides. Likewise, unplanned human slums and unregulated industries generate a lot of known and unknown emerging contaminants that pollute urban soils and water sources. Rapid urbanisation alters living styles and standards in the Mangaung Metropolitan Municipality (MMM). The MMM is faced with environmental challenges such as unplanned urban slums, incessant water and air pollution due to rapid urban development and human activities. Likewise, urbanisation in the study area triggered rural-urban migration that accelerate population growth in the study area; hence, the population rate in the MMM has shown an increase with numbers reported as 603 528 in 1996, 747 431 in 2011, 759 693 in 2016, 853 141 in 2018 and 861 651 in 2019. As such, this research sought to investigate the impact of rapid urban development in the MMM on water sources and environmental health sustainability. Systemic scientific methods were employed to investigate the urban land cover change, water quality and environmental health of the MMM. Remote sensing and geographic information systems were employed to analyse land use / land cover, Normalised Difference Vegetation Index, Normalised Difference Moisture Index, Normalised Difference Built-up Index and Normalised Difference Water Index changes for a period from 1978 to 2018 in the MMM. Furthermore, the historical water quality of important river systems and dams located on these rivers were studied to detect the impact of urban contamination. Consequently, the challenges accompanying rapid urbanisation in the MMM has led to the development of an urban health sustainability index to assess the status of environment health of the MMM. This is to ensure sustainability in all spheres of our environment and to mitigate the impact of urbanisation confronting us as people. The urban health sustainability index tracks a set of environmental and social environmental indicators that influence sustainability in an urban setting. The developed model observes the relationship between urban sprawl, land use / land cover changes, climatic variables, vegetation and water in terms of its sustainability. Furthermore, this research simulates the future land cover classification focussing on the urban growth development and water sources availability for the years 2028 and 2038. The result of the land use / land cover from satellite imagery revealed that an exponential increase in urban areas led to loss of vegetation cover and shortage of water availability in the MMM. This suggests that urbanisation accelerates the loss of vegetation cover, thus causing an increase in temperature and reduction in the amount of rainfall, thereby reducing the surface water quantity in the MMM. The change detection analysis observed between 1978 and 2018 revealed that agricultural areas increased by 22.6%. This can be linked to the increase in population growth and the upsurge in demand of farm products in the MMM. In addition, the Water Quality Index (WQI) of most of the water sources revealed deterioration in water quality from 1988, with a WQI of 20.1, 23.2 and 18.6 indexed as excellent, to 2018 with a WQI of 25.6, 41.0 and 49.0 indexed as good. This suggests the impact of urbanisation on water sources in the MMM. Conclusively, the results from the land cover classification and water quality assessment informed that the expansion in agricultural areas to enhance food security has led to the generation of more contaminants polluting the urban water system in the MMM. The urban health sustainability classification in the MMM ranged from low (30–50) to high (65– 80) sustainability scores. The low sustainability class is typical of areas with a high concentration of built-up areas, agricultural landmass and human activities where pollutants are mostly generated. Meanwhile, the high sustainability class is typical of areas with lowgenerating polluting media to the atmosphere and water sources. Likewise, the comprehensive environmental pollution index method categorised selected areas in the MMM into high, moderate and low polluted areas with index scores of 51–68, 42–44 and 32–37, respectively. The high and moderate polluted areas should be kept under environmental monitoring and pollution control for sustainable environmental health. The research recommends that control measures should be implemented in the township and urban slums in the MMM to reduce generation of solid waste through mandatory regulation and education. Policymakers in the MMM should curtail increases in unplanned settlements and control internal migration. This is to meet the urban sustainability goal by 2050 as campaigned by the United Nations. Finally, an environmental geochemistry study should be carried out to trace the sources of emerging contaminants across the MMM.