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Accueil du site → Doctorat → Danemark → Urbanization, urban climate and influence of vegetation. The case of cities in Ethiopia

University of Copenhagen (2013)

Urbanization, urban climate and influence of vegetation. The case of cities in Ethiopia

Feyisa, Gudina Legese

Titre : Urbanization, urban climate and influence of vegetation. The case of cities in Ethiopia

Auteur : Feyisa, Gudina Legese

Université de soutenance : University of Copenhagen

Grade : Doctor of Philosophy (PhD) 2013

Résumé partiel
This PhD thesis deals with urbanization-induced changes in land use/cover (LULC), associated local-level warming and the role of vegetation in mitigating the local thermal climate change in cities of Ethiopia. The thesis consists of four research papers that address these environmental changes and consequent problems. Through these papers, the project contributes to : 1) the science of remote sensing and Geographic Information System (GIS) by introducing methods that improve LULC classification accuracies, and an improved method of spatial thermal climate analyses, 2) better understanding of urban warming in tropical dry climates and effects of different urban vegetation in mitigating local warming, and 3) knowledge of human bioclimatology in a tropical warm climate by examining influences of urban thermal environment on workplace comfort and wellbeing. The changes in urban LULC as well as anthropogenic heat releases in cities, often lead to a local thermal climatic change described as an Urban Heat Island (UHI) effect. In tropical warm climate environments, additional warming caused by the UHI effect may intensify the already warm climate and may have detrimental effects on human health, socio-economic activities and general wellbeing. Worsening the UHI effects, the rapid urbanization in developing countries seems to ignore the immediate and long term impacts of the changes LULC on human and general ecosystem functioning. This could be evidenced by the haphazard urban expansion in many cities of developing countries, intensifying areas of impervious surfaces and shrinking of green spaces within cities and the surrounding landscape (Jorgenson et al. 2010 ; Kumar et al. 2010). Despite a large and increasing literature on the problems of urban environmental changes, a limited amount of such research has addressed thermal consequences of the ongoing rapid urbanization in African contexts. The magnitude of UHI and its impacts on human comfort and wellbeing, as well as effectiveness of urban vegetation in mitigating the UHI effects in the context of tropical Africa, are rarely studied. This project, therefore, contributes to the research gaps by considering examples from two cities in Ethiopia, namely Addis Ababa and Adama. The major sources of data used in this study were remotely sensed multi-temporal digital imagery from Landsat TM and ETM+ sensors, ground surveying of LULC, measurements of air temperature and humidity, and questionnaire surveying. Remote sensing and GIS techniques were applied to analyze urbanization-induced dynamics of LULC and associated urban warming in five-year intervals between 1985 and 2010. LULC dynamics were analyzed applying post-classification change analysis using the Landsat imagery. In relation to the use of Landsat data for LULC mapping, problems related to classification accuracy and consistency were detected during the initial phase of the project.


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