Urban Expansion and Loss of Agricultural Land: a GIS based study of Kiambu County

Urbanization leads to the outward expansion of cities and results in changes in land use and the dramatic effects are very clear in peri-urban areas. A key challenge of the urbanization process is the rapid conversion of prime agricultural land to urban land use (residential, industrial, and infrastructural construction) in the urban periphery. The present study attempts to understand the spatiotemporal extent of urban expansion and its implications on land use, by using remote sensing and GIS tools to detect land use/cover changes in a peri-urban setting over 28 years. Land use and land cover (lulc) maps were derived from Multispectral images of 1986, 2002 and 2014 from Landsat Thematic Mapper, Enhanced Thematic Mapper and Landsat 8. The study revealed a significant change of land-use/cover between 1986 and 2014 with the area experiencing a rapid increase in urbanization (41.6 %), forest decreased by (10.3 %), and a decrease in bare land (1.8 %), water (0.22 %) and agricultural area (29.3 %). Agricultural in 28 years is losing to urbanization with the results showing that 61.5 % of agricultural land converted to built-up land. From the research results, it's confirmed that there has been significant land use/cover change in the study area. Agricultural land being on a continuous decline, paving the way for urban developments, mainly associated with the expansion of settlements because of population increase and proximity to Nairobi city. These changes have had negative effects and positive outcomes on agricultural land use. With the increasingly high demand for land for construction of both commercial and residential developments also infrastructure such as road networks. The results also revealed that more land-use and cover changes are likely to take place as more land is converted over time, forest to agricultural land, and agricultural land to built-up land, which threatens the existence of agricultural land and the overall environment. Urban expansion at the expense of agriculture land reveals that the urban containment policies have been ineffective. Agriculture is crucial in terms of employment, food security. The continuous conversion and fragmentation of farms are resulting in the loss of the traditional economic base. In the growing population, it’s important to conserve and protect the potential farmlands, vertical expansion should be promoted. Good planning and a total paradigm shift in space management are necessary for the study area and the county at large, for sustainable development and food security. Agricultural land with good red volcanic soils should not be converted for urban and other land uses. Instead, innovative space optimization techniques should be adopted in locating residential and commercial buildings. With the research study results showing a strong linkage between urbanization and loss of agricultural land, we can conclude is that if the current trends continue, there will be an increase in declining of land under agriculture. Therefore, this shows the importance of the research findings to planners, urban managers and decision-makers and of particular importance to the county government of Kiambu to take up actions and draft of policies to further control the rate of urbanization to minimize and reduce its impact on existing land uses/cover.