Dynamics of urban sprawl : applying a CA-based model to explore future development scenarios in Thessaloniki

This study explores the dynamics of urban sprawl through the application of DYNAMA, a Cellular Automata (CA) based model. The model simulates the urban land use expansion process in a disaggregated field of land units taking into account a set of local characteristics of cells and neighborhood interactions, as well as a wide range of demographic, accessibility, socioeconomic, environmental and urban planning data. The model is applied to explore scenarios of future development in at the urban agglomeration of Thessaloniki in Greece, an area presenting a recent sprawling process resulting to a gradual change of the traditionally highly compact and monocentric structure. First, the model logic and structure is presented. The model calculates combined urbanization potentials on the global and the local level and uses a stochastic process in order to allocate new urban land in the cell-space. Next, emphasis is placed on the calibration of the model in the study area and on the exploration of future development scenarios. The calibration of the model is based on an automatic calibration process on the CA level and on a multiple regression model which has been used to quantify the influence of macro-scale factors on the regional level. Urban land cover changes for the period 1990-2010 have been examined and the fit of the model to the observed data is evaluated. The model is then used to explore two different scenarios of urban development. The first scenario is based on current trends concerning urban land expansion rates and assumes that protected area policy and land use regulations will remain stable. In the second scenario we hypothesized a smaller urban land expansion rate and a policy restriction on building in agricultural land as well as an increase in the area of protected zones. From the comparison of the results we observe that in scenario-1, urban sprawl characterized by leapfrog development in the periurban zone is accelerated and that expansion of urban land uses in agricultural land and in the countryside remains intense. On the other hand, in scenario-2 a large part is incorporated inside existing boundaries and urban sprawl in environmentally important areas and fertile agricultural land is reduced.