Water is an essential resource for human settlement. Regardless of the climate or economy, if there is not an adequate supply of water to meet the water demands of a community, the community cannot be sustainable. Thus managing water supply and demand so that demand does not exceed supply will be an essential component of any communities plan for sustainability. Such management, referred to as water resources management, in urbanized regions can be very complicated. The systems used to collect water from multiple sources, treat it, deliver it to community residents, collect the wastewater, treat it, and safely dispose or reuse it are typically complex highly regulated systems often operated by multiple agencies over different geographies that can span hundreds of miles. Management of such complex systems is further complicated by the future uncertainty in the factors that affect water supply and demand. Such uncertainties include: possible changes in the future growth or decline of a community and the behavior of its residents to use water, possible change is future of climate conditions of the community, and the ability of government and private institutions to respond to these changes in a manner that maintains a balance between water supply and demand.
To better understand how these uncertainties affect the complex tasks of water resources management, the Decision Center for a Desert City has been using a water and supply demand model, called WaterSim. This model has been implemented for the Central Arizona region and used primarily in four ways:
- Understand the dynamic nature of managing a complex water supply and demand system for urban regions.
- Explore the effectiveness of various water management policies.
- Explore the uncertainty of regional growth and climate change by understanding the impact different growth and climate change scenarios may have on the region’s complex water system and management policies.
- Explore how people make decisions for highly complex problems that are subject to high uncertainty.
Currently, WaterSim is available for use by researchers, water policy managers, and the general public in three ways. WaterSim in the Decision Theater, WaterSim on the Web, and WaterSim API Version 5.0, a public domain model programming interface.
In DCDC II, we have continued to implement and refine our signature computer-simulation model, WaterSim, to investigate how alternative climate conditions, rates of population growth, and policy choices interact to affect future water supply and demand conditions in Phoenix. We designed WaterSim not only as a decision-support tool but as a hybrid boundary object designed to link science and policy to improve environmental decision making under conditions of uncertainty. As such, the modeling effort incorporates structured ongoing feedback from stakeholders and researchers.
WaterSim is a hierarchical model that uses supply from surface and groundwater sources and demand from residential, commercial, incorporating the rules that govern reservoirs, aquifer use, and land-use change. Gober et al. (2011) in Environment and Planning B and Sampson et al. (2011) in Journal of Environmental Management described the development of WaterSim. The current version of the model, WaterSim 5.0, is comprised of (1) a Microsoft C# interface; (2) a C# library module; and (3) a simulation model (FORTRAN) that houses the rules and algorithms to model water supply and demand, all at the water provider-level. WaterSim 5.0 runs on an annual time-step. WaterSim 5.0 produces water supply and use patterns for 33 Phoenix Metropolitan Area water providers.
DCDC II’s WaterSim Steering Committee developed recommendations for model improvements based on feedback from the research community and community partners. The new version of WaterSim, includes a Microsoft.Net-based standalone model (which does not require PowerSIM) with a documented application interface (API) and base condition data sets for Central Arizona.