The Urban Expansion of Nairobi City
非洲内罗毕城市变化的遥感监测与驱动因子分析

Nairobi is one of the fastest developing cities in Africa and urban areas are growing rapidly. Using remote-sensing to detect multi-temporal change, multispectral imagery has been developed over several decades;however, it is still difficult to select a suitable change-detection method, especially in urban areas. Here, we present a method using multi-temporal data to detect land-use change in an urban environment based on principal-component analysis (PCA) and hybrid classification methods. Three Landsat images (one scene of TM images in 1988, one scene of ETM in 2000 and one scene of TM in 2010) were used to explore the urban expansion of Nairobi City from 1988 to 2000. The results show that the built-up area has increased 141.24km2 from 1988 to 2010, 60.03km2 from 1988 to 2000 and 81.21km2 from 2000 to 2010. The total built-up area in 2010 was 1.27 times of that in 1988. Urban expansion has been accompanied by a loss of forests and urban sprawl. Rapid population growth, traffic infrastructure,government policies,and topographical and geological factors may be the driving this fast expansion. The road network has influenced the spatial patterns and structure of urban development, so that the expansion of the built-up areas has assumed an accretive as well as linear growth along the major roads. Analysis of urban sprawl directions and land use conversions indicates that deliberate planning is largely lacking in Nairobi's urbanization process, and that the general urban planning principles encoded in various laws and local government regulations have not been adhered to or enforced. The environmental and social consequences of a rapidly growing population in a poorly planned urban system have been dramatic. A better understanding of the spatial and temporal dynamics of this city 's growth will form the basis for better planning, understanding of the sustainable development situation and effective spatial organization of future development.