Monitoring high-quality soil consumption driven by urban pressure in a growing city (Rome, Italy)

The aim of this paper is to quantify the impact of urban expansion on soil quality in a sprawling Mediterranean region (Rome, Italy). The study verifies, at regional scale, if urban growth has consumed high-quality soil types at the expense of agricultural and forested land. At local scale, it tests if the recent urban diffusion has consumed more high-quality soil types than compact urban development. To verify these hypotheses, two high-resolution land-use maps for 1949 and 2008 were analyzed together with a 1:50,000 map of soil characteristics. Over an investigated area of 1500 km2, urban fabric increased by 5.9% per year (from 8.2% in 1949 to 36.6% in 2008). In that period, urban areas consumed high-quality soil types in larger proportion than low-quality soil types while croplands and forests progressively occupied low quality and partly degraded soil types. Moreover, dispersed peri-urban settlements have been developed in Rome on high-quality soil types more frequently than dense urban settlements, suggesting that the recent low-density expansion impacts largely soil quality and land resources. This confirms that sprawl consumes high-quality land at higher rate than compact growth, possibly influencing the environmental quality of neighboring areas. Finally, the role of soil quality as a target for policies mitigating land consumption in ‘shrinking’ Mediterranean cities is discussed.

► Croplands and forests progressively occupied low-quality and partly degraded soils.
► Residential urban sprawl consumes more high-quality soils than compact growth in Rome.
► Soil consumption can impact landscape resilience and ecosystem stability.