GeoJournal DOI 10.1007/s10708-016-9719-x Quantifying the spatio-temporal patterns of settlement growth in a metropolitan region of Ghana Ransford A. Acheampong . Felix S. K. Agyemang . Mohammed Abdul-Fatawu Ó The Author(s) 2016. This article is published with open access at Springerlink.com Abstract Retrospective understanding of the mag- increase occurred in the last 13 years alone, with UEII nitude and pace of urban expansion is necessary for value of 0.605 indicating a moderate intensity of urban effective growth management in metropolitan regions. expansion. Moreover, the metropolitan-core of the The objective of this paper is to quantify the spatial– sub-region, being the focal point of urban develop- temporal patterns of urban expansion in the Greater ment and the historical origins of expansion, Kumasi Sub-Region (GKSR)—a functional region accounted for more than half of the total built-up land comprising eight administrative districts in Ghana, increase over the 28-year period. Over the last decade West Africa. The analysis is based on Landsat remote and half however, urban expansion has spilled into the sensing images from 1986, 2001 and 2014 which were neighbouring peripheral districts, with the highest classified using supervised maximum likelihood algo- intensity and fastest rate of expansion occurring in rithm in ERDAS IMAGINE. We computed three districts located north and north east of the sub- complementary growth indexes namely; Average regional core. We recommend a comprehensive Annual Urban Expansion Rate, Urban Expansion regional growth management strategy grounded in Intensity Index (UEII) and Urban Expansion Differ- effective strategic partnerships among the respective entiation Index to estimate the amount and intensity of administrative districts to curb unsustainable urban expansion over the 28-year period. Overall, urban expansion. expansion in the GKSR has been occurring at an average annual rate of 5.6 %. Consequently, the sub- Keywords Urbanization Á Urban expansion Á Spatio- region’s built-up land increased by 313 km2 from temporal change Á Landsat Á GIS Á Greater-Kumasi Á 88 km2 in 1986 to 400 km2 in 2014. The analysis Ghana further show that about 72 % of the total built-up land R. A. Acheampong (&) Á F. S. K. Agyemang Introduction Lab of Interdisciplinary Spatial Analysis, Department of Land Economy, University of Cambridge, 19 Silver Street, Cambridge CB3 9EP, UK Rapid and unfettered urban expansion constitutes one e-mail: [email protected] the visible manifestations of the on-going urbanization process in cities of the Global South. The growth of M. Abdul-Fatawu urban areas in these regions have been fuelled by the Faculty of Geo-Information Science and Earth Observation, University of Twente, 7500 AE Enschede, demographic processes of natural population growth The Netherlands and rural–urban migration as well as the 123 GeoJournal reclassification of previously rural settlements into satellite platforms, providing quality land cover data at urban centres (Potts 2012; UN-Habitat 2010). spatial and temporal resolution required for land-use In broad terms, urban expansions could be cate- change studies. A number of challenges exist in using gorised into the three interrelated processes of infill- satellite imagery to detect land use change, including ing, expanding, and outlying (Wilson et al. 2003). the many combinations of materials present and the Infilling results in relatively compact and consolidated variations in size or shape of urban features that can physical development. In most cities in developing lead to different ‘mixtures’ within pixels (Schneider countries however, rapid peri-urbanization, charac- 2012; Xian and Crane 2005). Notwithstanding, com- terised by unconsolidated lateral physical expansion bined with Geographical Information Systems (GIS), and sprawl, has resulted in existing built-up areas Landsat satellites have provided multi-spectral and engulfing smaller towns on their peripheries (Webster multi-temporal data that have been used extensively 2002; Kombe 2005; Doan and Oduro 2012). As for land cover mapping, environmental modelling and contemporary form of urbanization, the uncontrolled land use modelling (e.g. Schneider 2012; Masek et al. expansion of urban centres into their peripheries has 2000; Wakode et al. 2014). been driven by the need to accommodate rapid In this paper, we use Landsat remote sensing population growth and to meet the attendant space imagery from 1986, 2001 and 2014, GIS analytical demands of various socio-economic activities often at techniques and spatial metrics to quantify the spatio- the expense of Greenfield land (Acheampong and temporal patterns of urban expansion within the Anokye 2013; Appiah et al. 2014; Owusu-Ansah and Greater Kumasi Sub-Region (GKSR) in Ghana. The O’Connor 2006). GKSR is a newly designated, rapidly urbanizing Although there is emerging evidence that suggests metropolitan region in Ghana, comprising the Kumasi that urbanization particularly, in Sub-Saharan Africa metropolis, the country’s second largest metropolitan has been occuring very slowly or even stagnated (Potts area, and seven peripheral districts. In recent years, a 2012), there is a general consensus that its accumu- number of empirical studies have sought to understand lated impacts over the years, poses various challenges urban expansion trends in the sub-region. Using to urban growth management and sustainable devel- OpenStreetMap and Google Earth, Oduro et al. opment. The emerging challenges of climate change, (2014), analyzed drivers of urban growth in the sub- environmental degradation and resource depletion region. Cobbinah and Amoako (2012), estimated resulting from decades of rapid urbanization (Watson historical land-use distribution in the Kumasi metro- 2009), pose serious threats to public health, the polis—the historical core of the sub-region between continuous supply of essential eco-system services 1995 and 2010. Other studies have addressed urban and food security (Eigenbrod et al. 2011; Baloye and expansion and its implications in selected peri-urban Palamuleni 2015). towns in the sub-region (e.g. Acheampong and Anokye Gaining a retrospective understanding of the spatio- 2013; Amoateng et al. 2013; Appiah et al. 2014). temporal urban land-use dynamics and the underlying While some of these previous studies have provided driving-forces is crucial to managing growth to avert descriptive analysis of the reasons driving rapid peri- unstainable urban expansion and the associated neg- urban development in the sub-region based on survey ative impacts. Adequate and reliable data through data (e.g. Acheampong and Anokye 2013; Owusu- conventional surveying and mapping techniques have Ansah and O’Connor 2006), others have relied on data however, been either unavailable, limited in scope, from government departments obtained from existing expensive or time consuming to acquire for accurate land-use plans and/or through conventional mapping analysis of historical urban expansion at different techniques such as field-updates (e.g. Amoateng et al. spatial scales (Jat et al. 2008). 2013; Cobbinah and Amoako 2012). Data from land In recent years, land use changes in many countries use plans, for example, allows to estimate detailed have been monitored and predicted at the national, land-use distributions in areas covered by planning regional and city scales using satellite remote sensing schemes. However, relying on this alone could imagery (e.g. Wakode et al. 2014; Xu et al. 2007). underestimate the quantum of built-up land in the Among the commonly used satellite sensors is the study area since in Ghana, for example, land use plans Thematic Mapper (TM) on board the Landsat series can provide data only for areas covered by planning 123 GeoJournal schemes. Moreover, owning to the lack of frequent an increase in the quantum of built-up land of a spatial updates of these land use plans by the physical unit through the combination of horizontal and vertical planning departments, data derived from them is often development at varying densities. The expansion of unreliable and fraught with accuracy problems. urban areas take place in substantially different forms The current paper builds on the empirical insights in different contexts which makes it difficult to accrued over the years from these initial research. Our propose any single theoretical model, either descrip- approach and contribution, however differs consider- tive or analytical to explain the phenomenon. ably from these initial works in terms of the spatial Although classical models of urban spatial structure, extent of the analysis, temporal scope, data sources grounded in urban micro-economics, offer useful and methodology. This study, constitutes the first theoretical insights into how cities grow and the attempt to apply Landsat satellite data and spatial general emergent patterns of land uses (see e.g. Alonso metrics to quantify historical urban expansion at the 1964; Burgess 1925), these models seem constrained macro (i.e. sub-regional) and micro (i.e. district-level) to their specific cities of origin. Moreover, they scales over a period of 28 years. address a broad range of urban growth phenomenon The remainder of the paper is organized as follows: and are unable to account for the different manifes- In the section that follows, we discuss the typology and tations of physical urban expansion. manifestations of urban expansion to set the frame- In the absence of a general theoretical model, work