Urban Impact at the Urban-Agricultural Interface in Madison, WI: an Ecosystem Modeling Approach

Global population and the proportion of people living in urban areas both continue to grow while average urban density is decreasing worldwide. Because urban areas are often located in the most agriculturally productive lands, expansion of the built environment can cause sharp reductions in land available for cultivation. Conversion of land to urban use also significantly alters climate variables. Urban materials differ from natural land covers in terms of albedo, thermal properties, and permeability, altering energy and water cycles. Anthropogenic heat emissions also alter the energy balance in and around a city. Preliminary analysis of urban impacts around Madison, WI, a small city located in a thriving agricultural region, was performed using the National Land Cover Database (NLCD), MODIS albedo products, ground-based observations, and a simulation of urban expansion, within a geographic information system (GIS). Population of the county is expected to increase by 58% while urban density is projected to decrease by 49% between 1992 and 2030, reflecting projected worldwide patterns. Carbon stored in the top 25cm of soil was found to be over 2.5 times greater in remnant prairies than in croplands and was calculated to be even less in urban areas; projected urban development may thus lead to large losses in carbon storage. Albedo measurements also show a significant decrease with urban development. Projected urban expansion between 2001 and 2030 is expected to convert enough agricultural lands to urban areas to result in a loss of 247,000 tons of crop yield in Dane County alone, based on current yields. For a more complete analysis of these impacts, urban parameters are incorporated into a terrestrial ecosystem model known as Agro-IBIS. This approach allows for detailed comparison of energy balance and biogeochemical cycles between local crop systems, lawns, and impervious city surfaces. Changes in these important cycles, in soil carbon storage, and in crop productivity/yield for 1992 - 2001 and projected 2030 development around Madison, WI will be shown.