Generating policies for sustainable water use in complex scenarios: An integrated land-use and water-use model of Monroe County, Michigan

Rapidly declining groundwater levels in Southeast Michigan have raised serious concern since the early 1990s. Hydrological studies suggest that land-use changes have caused this decline. The mechanisms linking land-use and groundwater dynamics are not clear, however. To examine this link, I developed the Water-Use Land-Use Model (WULUM), an agent-based model that serves as an analytical framework to understand how these processes interact to create the observed patterns of resource depletion, and to suggest policies to reverse the process. The agent-based model is empirically based on Monroe County, Michigan, and informed with land-use and survey data and expert knowledge about the case. The land-use component includes the main groundwater extractors in the county: stone quarries, golf courses, farms and households. The groundwater component includes the glacial deposits and the underlying bedrock aquifer. The behavior of water users is defined by simple rules that determine their location and consumption decisions. The dynamics of groundwater are represented through simple diffusion rules between each cell and its immediate neighbors.; Scenario-based simulations provided the medium for exploratory analysis of the integrated land-use/groundwater system. Pre-testing of WULUM highlighted the importance of the glacial recharge rate of the aquifer in determining the regional hydraulic gradient, recommending reexamination of the parameter values cited in literature. Although quarries extract 75 percent of the total withdrawal, simulations showed that eliminating quarry dewatering did not entirely reverse groundwater decline. Urbanization, on the other hand, contributed significantly to long-term decline. Both low-density and high-density zoning restrictions improved aquifer conditions over medium-density development, suggesting a non-linear relationship between intensity of residential use and groundwater levels. Moreover, of all the natural and policy variables, zoning had the greatest influence on urban settlement and therefore on resource consumption. Medium to high values of hydraulic conductivity in some cases reinforced drought conditions by extending the area affected by excess withdrawals, so that land-use policies should discourage residential concentration in those areas.; Thus, while quarries currently affect large areas, expanding suburbanization may lead to regional groundwater depletion in the near future, depending on the spatial distribution and the intensity of development.