SCENARIO ANALYSIS FOR THE SAN PEDRO RIVER, ANALYZING HYDROLOGICAL CONSEQUENCES OF A FUTURE ENVIRONMENT WILLIAM G. KEPNER1*, DARIUS J. SEMMENS2, SCOTT D. BASSETT3, DAVID A. MOUAT3, and DAVID C. GOODRICH2 1 U.S. Environmental Protection Agency, Office of Research and Development, P.O. Box 93478, Las Vegas, Nevada 89193 USA; 2USDA Agricultural Research Service, Southwest Watershed Research Center, 2000 E. Allen Road, Tucson, AZ 85719 USA; 3 Desert Research Institute, Division of Earth and Ecosystem Sciences, 2215 Raggio Parkway Reno, NV 89512 USA (* author for correspondence, phone: 702-798-2193, fax: 702-798-2208, e-mail: [email protected]) Abstract. Studies of future management and policy options based on different assumptions provide a mechanism to examine possible outcomes and especially their likely benefits and consequences. The San Pedro River in Arizona and Sonora, Mexico is an area that has undergone rapid changes in land use and cover, and subsequently is facing keen environmental crises related to water resources. It is the location of a number of studies that have dealt with change analysis, watershed condition, and most recently, alternative futures analysis. The previous work has dealt primarily with resources of habitat, visual quality, and groundwater related to urban development patterns and preferences. In the present study, previously defined future scenarios, in the form of land-use/land-cover grids, were examined relative to their impact on surface-water conditions (e.g., surface runoff and sediment yield). These hydrological outputs were estimated for the baseline year of 2000 and predicted twenty years in the future as a demonstration of how new geographic information system-based hydrologic modeling tools can be used to evaluate the spatial impacts of urban growth patterns on surface-water hydrology. Keywords: alternative futures analysis, hydrologic modeling, watershed assessment, geographic information systems, landscape indicators, landscape characterization, remote sensing, regional vulnerability, San Pedro River 1. IntroductionThe assessment of land use and land cover is an extremely important activity for contemporary land management. A large body of literature (e.g., Houghton et al., 1983; Turner, 1990; McDonnell and Pickett, 1993) suggests that human land-use practices (including type, magnitude, and distribution) are the most important factors influencing natural resource management at local, regional, and global scales. Today’s environmental managers, urban planners, and decision-makers are increasingly expected to examine environmental and economic prob-lems in a larger geographic context. To accomplish this, it is necessary to 1) understand the scale at which specific management actions are needed; 2) conceptualize environmental management strategies; 3) formulate sets of alternatives to reduce environmental and economic vulnerability and Environmental Monitoring and Assessment 94: 115–127, 2004. �2004 Kluwer Academic Publishers. Printed in the Netherlands. c116 KEPNER ET AL. uncertainty in their evaluation analyses; and 4) to prioritize, conserve, or restore valued natural resources, especially those which provide impor-tant economic goods and services. A scenario-based approach to regional land planning offers an orga-nizational basis to explore decision analysis and opportunities for public resources. Scenario planning was initially used by the military after the Second World War and has since been tested in a variety of geographical settings to assist stakeholders and policy makers in shaping future use of land and water resources (Schwartz, 1996; Steinitz, 1990). Compared with other assessment frameworks, scenario analysis offers several advantages, including the ability to intentionally investigate several “futures” or different points of view at one time. The most important reasons for employing scenario analysis relate primarily to the potential benefits of evaluating all aspects of the local decision-making processes. For example, for land owners interested in protecting their property rights, scenario analysis can be used to understand the range of potential impacts to their lands that may be caused by regional change relative to the type, location, and magnitude of proposed management actions or policy. Additionally, for elected officials and public administrators, scenarios can be used to test current planning ideas in terms of public perceptions or presumed demographic changes. Thus, scenarios can be used to test the resilience of plans against assumptions about the stability and growth into the future. Lastly, the use of scenarios allows members of an entire community to assess the relative impacts of several alternative sets of choices for a desirable future environment. Scenario analysis thus requires that scenarios be possible, credible, and relevant to be useful in decision-making processes. This paper presents the results of a study that examines the impact of urban development in a semi-arid environment relative to sustainability of water resources, its most crucial asset. In particular, it attempts to answer questions that relate to future scenarios that describe extremes in position (e.g., development options that are most development and least conserva-tion oriented and vice versa) with the idea that urban growth patterns can be managed to minimize hydrologic and environmental impacts. 2. Materials and MethodsLandscape architecture involves several areas of theory, all of which influence design. Much of the contemporary thinking in regard to117 SCENARIO ANALYSIS FOR THE SAN PEDRO RIVER landscape design analysis has been outlined in various studies performed at the Harvard University Graduate School of Design (Steinitz et al., 2003, 2000, 1996, 1993, 1990). In these studies potential impacts from a number of wide-ranging scenarios are compared to current conditions of a region in terms of a set of processes that are modeled in a geographic information system (GIS). Alternative future landscape analysis involves describing the patterns and significant human and natural processes affecting a geographic area of concern, constructing GIS models to simulate these processes and patterns, creating changes in the landscape by forecasting and by design, and evaluating how the changes affect pattern and process using models (USEPA, 2000). The application of several advanced technologies to assess the