Assessment of landscape change and occurrence at watershed level in city of Nairobi
To ecologically manage urban spaces, it is necessary to understand changes in spatial configuration of land uses within definitive ecosystem level processes. Change in landscape cover types and pattern within Nairobi city and its environs were investigated using landsat satellite data spanning three decades. Image data were georeferenced, classified and analyzed along watershed zones delineated from a digital elevation model (DEM) of Nairobi city and peripheral region on a geographical information system (GIS) platform. Land cover categories of riverine vegetation and forest land showed the most marked decrease in areal coverage by about 67 and 60%, respectively, while barren surfaces and urban areas increased by more than 100 and 98%, respectively, between 1976 and year 2000. At the watershed scale, land cover diversity was high in the upper and middle basins than on the lower basin of the watershed zones. Expansion of urban areas was confined mainly in the middle elevation watershed zones. Forest area declined notably in the central watersheds while savannah areas increased towards the southern watershed zones. Monitoring land cover change at the watershed scale is more indicative of impact level and where efforts for managing and conserving the urban landscape should be prioritized.
Key words: Urban expansion, land cover type, remote sensing, watershed units, urban landscape conservation.