Urban expansion constitutes one of the key agents of land use change with the impact felt at local, regional and global levels, such impact include spatial growth on agricultural land. This study assesses urban encroachment on agricultural land in Offa Local Government Area of Kwara State, Nigeria using Remote Sensing and Geographic Information techniques. Three imageries of LandSat TM 1990, LandSat ETM 1999 and Nigeria Sat X 2014 used processed, classified using supervised classification, and analyzed in Erdas Imagine 9.2 and ArcGIS 10.1 environment to assess the total spatial loss of agricultural land to urban expansion. Built – up and Agricultural land were extracted from the imageries and the spatial growth and loss within the study period was established. The findings revealed that the study area witnessed a significant reduction and increase in agricultural land and built – up respectively. Agricultural land occupying the highest coverage of 148.63 km² (65.36%) in 1990 decreased to 107.18 km² (47.14%) in 2014. The total spatial loss was 41.45 km² (27.89%) at an annual rate of 1.73 km² within the same period. While the built-up area expanded from 17.5km² in 1990 to 65.09 km² in 2014, total spatial change of 47.52 km² (270.40%) was experienced with at annual rate of 1.98 km² (11.27%) within the study period (1990 – 2014). The comparison of these results shows that 43.50 km² (19.13%) of agricultural land in the study area was lost to urban expansion within the study period at an annual conversion rate of 1.81 km². From the foregoing, it is recommended that urban spreading to agriculture land should be controlled as this will have serious repercussions on food security, although urban expansion cannot be stopped, but with proper management and planning it can be directed in a desirable and sustainable way.
1.1BACKGROUND TO THE STUDY
The world is rapidly urbanizing, and it has witnessed a tremendous shift of its population from being predominantly rural to predominantly urban in the last two decades (De Sherbinin, 2007). The world’s population is estimated to be 7.01 billion and by the year 2030, more than 60% of this population will be living in urban areas especially in developing countries, consuming close to three-quarters of the world‟s natural resources, and generating three quarters of its pollution and wastes (Peters, 2000; Redman and Jones, 2005). This growth will require unprecedented investment in new infrastructure and create serious challenges for political and social institutions.
Rapid expansion of urban centers in the world at large and specifically in developing countries has continued to pose great challenges such that evokes interests from ecologists, planners, civil engineers, sociologists, administrators and policy makers on how much expansion is taking place, the effects on agricultural land and possible solution. It serves as a strong agent of land use/land cover change, hence loss of agricultural land (Olawole, Msimanga, Adegboyega, and Adeshina, 2011), and equally contributes to development; a requirement for and a result of economic, cultural and social development, as well as engines of economic growth and poverty alleviation (World Bank, 2009).