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A land-cover based urban dispersion indicator suitable for highly dispersed, discontinuously artificialized territories: The case of continental Portugal

Urbieta, Pablo, Fernandez, Emilio, Ramos, Luís, Méndez Martínez, Gonzalo, Bento, Ricardo
Land use policy 2019 v.85 pp. 92-103
arable soils, carbon sequestration, environmental impact, hinterland, land cover, land use, public policy, temporal variation, urban planning, urbanization, Portugal
Land-cover based indicators assessing the effect of the magnitude and spatial patterns of the artificialization process, including urban sprawl, barely consider the impact of the discontinuous spatial distribution of the artificialized built-up areas. In this study, we propose a new urban dispersion indicator, which incorporates the characteristic dynamics of the discontinuous urban artificial land cover class, characteristic of scarcely populated and highly dispersed territories, such as is the case of Continental Portugal. The indicator is based on the premise that the more built-up area, the higher the uptake of constructed area in a discontinuous pattern and the more dispersed this built-up area, the lower urban sustainability of the territory. Given that the minimum cartographic unit in Corine Land Cover (25 ha) is typically higher than most of the discontinuous urban patches in these territories, in this research we used national land use data from Portugal with a minimum cartographic unit of 1 ha.The values calculated for this indicator show that the level of urban dispersion of continental Portugal increased by 14.2% in the 1990–2007 period. The artificialization process was geographically heterogeneous with notable differences being observed between regions and also along the urban to rural and coastal to hinterland gradients. The temporal changes in the indicator allowed the identification of distinct artificialization patterns: diffusion, sprinkling and coalescence, which were interpreted on the basis of the evolution of the artificialization process. The values derived from this indicator were related with two main environmental impacts associated with the artificialization process: the loss of arable land and the decrease in the carbon sequestration capacity of the territory. The proposed indicator can be a useful tool to monitor and evaluate the impacts of different public policies with a direct impact on land artificialization, as well as on the territorial and urban planning processes, whether at the national, regional or municipal level, allowing more detailed and consistent spatial analyses and diagnoses of urban sustainability to be undertaken.