System dynamics modeling in local water management : assessing strategies for the city of Boerne, Texas

Hydrologic systems, despite their complexity, have remained relatively balanced throughout time, but as climate changes and as population exerts more pressure onto water sources, these systems may be altered in ways that are difficult to predict. As Texas’ climate becomes hotter and drier, water deficits can become widespread as sources are strained beyond their capacity. For small areas, like the City of Boerne, Texas, water management and planning is a way to prepare for shortages that may occur in the future. To create a water management plan that increases the city’s resilience and sustainability, Boerne must understand its current water system and how it will change in the future. The balance between water supply and demand is conceptualized through the use of causal loop diagrams and then through system dynamics modeling. Three interventions are used as disruptions to the system: xeriscaping, adoption of rainwater harvesting systems, and adoption of smart meters for residential irrigation. Each strategy is varied across range of adoptions. The resulting 125 different combinations are analyzed under three scenarios: a base case assuming the city’s maximum supply of water is firm, and two different responses to a meteorological drought. Results show that the city can effectively reduce total demand, forestalling the point at which it surpasses supply. Different combinations of adoptions can achieve the same goal, giving the city optionality in choosing strategies that are most suited for their needs and constraints. Rainwater harvesting was found to be the dominant intervention influencing demand. Though effective in the base scenario, the influence of rainwater harvesting is less in the two drought scenarios given its dependence on precipitation. Xeriscaping was the second most influential intervention and smart meters for irrigation had no effect on demand. The approach used in this study highlights the interdependency between community adoption of conservation strategies and the importance of considering these relationships using systems modeling