Saturday, 15 July 2006

Quantifying Sprawl and its Threat to Prime Farmland.

Maaike J. Broos and Rick L. Day. Penn State Univ, 116 ASI Building, University Park, PA 16802

Prime farmland is very important to agriculture. However, as prime farmland is not only very suitable for growing crops, but also for “growing” houses, much prime farmland is lost to development. The most recent data from the National Resources Inventory show that between 1992 and 2001 about 2.4 million hectares (28%) of the newly developed land in the United States was prime farmland and that the conversion rate increased from an average of 0.16 million hectares per year between 1982 and 1992 to 0.24 million hectares per year between 1992 and 2001. Much of this new development takes the form of low-density sprawling development. (Sub)urban sprawl is a much discussed issue. This illustrates the significant amount of public concern about the impact of sprawling development patterns. Many (negative) consequences, including loss of (prime) farmland and open space, reduced agricultural productivity, loss of wildlife habitat, increased water and air pollution, reduced groundwater recharge due to increased impervious surface, traffic congestion, etc. have been associated with sprawl development. To help clarify the debate on sprawl and to improve planning and policy making there is a need for consistent and repeatable measures of sprawl that may be linked to specific (alleged) effects of sprawl. Currently, few sprawl metrics are available that may be used to describe sprawl at a local (county or municipal) level. The problem starts with the definition of sprawl. Despite the massive amount of literature discussing sprawl, relatively few people have attempted to operationally define sprawl, a requirement for the measurement of the level of sprawl. Also, existing metrics are often based on the use of (highly) aggregated datasets, which do not allow for the analysis of more finely grained patterns within the developed landscape. Finally, most sprawl studies focus exclusively on major metropolitan areas and cities, so very little information is available on how these sprawl indices perform in the suburban fringe or in exurban and rural areas. Sprawl development, however, does not occur exclusively in urban areas. Increasingly, the need for a better understanding of the spatial and temporal dynamics of development in suburban and exurban areas is recognized as many natural resources such as prime farmland as well as sensitive environmental lands in those areas are threatened by sprawling development. The aim of this study is to define and evaluate sprawl metrics that use geospatial technologies and detailed local digital datasets to carefully measure and track sprawl at a local level along the full spectrum of development (urban, suburban, and rural). Multiple GIS-based sprawl indices evaluating the pattern of land use and development will be presented and discussed. These indices measure the degree to which development is sprawling in various dimensions: density, continuity, concentration, clustering, centrality, nuclearity, mixed uses, and proximity. The identification of various sprawl dimensions allows for the quantification of different types of sprawl development. All sprawl indices will be illustrated using a case study for several counties in Pennsylvania, USA. The sprawl indices will then be related to some of the effects of sprawl on agriculture such as the (potential) loss of prime farmland, decrease in agricultural productivity, and farmland fragmentation.

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