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Among factors causing soil degradation one of the most important, although less studied in Mediterranean environments, is the irreversible loss of soil due to urbanisation processes, inserted into the more general concept of soil sealing. In coastal Mediterranean regions, such as the Valencia Region, Spain, land cover transformations are mainly produced by contemporary socio-economic changes that have produced a drift from traditional agriculture to industrial and tourism economies, reinforced by population's trends to concentrate in cities or larger urban regions. Evaluation of soil sealing is then a key element to understand soil degradation and the disappearance, in most cases, of highly productive soils.

This work, inserted within a major study on land use-cover change and soil degradation of metropolitan areas in the Valencia Region, presents the preliminary results on the urban-non urban (open agrarian and natural spaces) dynamics in the municipality of Alicante, the second largest city in the region. Three sets of panchromatic air photos for the years 1956, 1985 and 1998 have been used. After air photo scanning, on screen digitising using a base digital topographic map at scale 1 : 10,000, was applied to extract two major types of soil cover: agrarian and urban. A Geographical Information System vector structure has been implemented for cartographic comparison. Finally, to identify spatial and temporal changes maps and overlays together with synthetic tables were produced in order to assess soil degradation.

Results show that there has been a substantial loss of soil devoted mainly to agriculture. Urban growth can be differentiated into three distinct spatial patterns: 1) edge compact enlargement of the city boundaries, including growth following the main road network; 2) compact new urbanisation alongside the coast and 3) the colonisation by groups of individual residences mainly over continental open spaces. One of the main impacts of such new urban pattern has been the loss of the most fertile soils distributed over the alluvial plains around the city, which has been mainly occupied by the tourist and residential buildings.