Resumen
Ensuring water availability for multiple needs represents a sustainable development challenge globally. Rigid planning for fixed water supply and reuse targets with estimated demand growth and static assumptions of water availability can prove inflexible in responding to changing conditions. Formal methods to adaptively respond to these challenges are needed, particularly in regions with limited natural resources and/or where multiple uncertain forces can influence water-resource availability and supply reliability. This paper assesses the application of Scenario Planning in one such region?Tucson, Arizona, USA?over the coming 40 years, and highlights broader lessons for addressing complex interrelationships of water management, infrastructure development, and population growth. Planners from multiple jurisdictions and researchers identified ten key forces and prioritized three with the greatest uncertainty and the greatest impact for water and development planning: (1) changing demands based on potential future density, layout, and per capita water use/reuse; (2) adequacy of current water supplies to meet future demands; and (3) evolving public perceptions of water reuse including potential options to supplement potable water supplies. Detailed scenario modeling using GIS and infrastructure cost optimization is under development and is now beginning to produce results, to be discussed in future publications. The process has clearly demonstrated the value of Scenario Planning as a tool for bringing stakeholders into agreement over highly complex and historically divisive problems, and for prioritizing amongst diverse uncertainties. The paper concludes by characterizing possible outcomes for this case and draws lessons for other water scarce regions experiencing rapid development.