Sociohydrology of an Arid City: Development of a Coupled Model of Water Management in Las Vegas

Rapidly growing cities in arid regions present a significant water management challenge. Key to tackling this challenge is understanding how and why some cities transition to more sustainable water management; acknowledging that urban water resources decisions are both responding to and precipitating hydrologic change, this question is best tackled through a sociohydrology approach. While coupling of natural and societal systems is in it’s infancy in the field of hydrology, there is a strong tradition of studying coupled systems in the field of Socio-Ecological Systems. We build on Ostrom’s Socio-Ecological Systems framework to develop a system dynamics model of water management for the Las Vegas metropolitan area using Vensim. A key objective our proposed modeling framework is to illuminate the dynamic interactions of the sociohydrologic system components and enable testing of various assumptions and strategies.

The model of Las Vegas water management consists of five sub-modules: water supply, water demand, finances, public perception and policy making process. The development of the first three modules were based on clearly defined system structure. The public perception sub-module tracks the level public risk perception of a water supply shortage and represents the hypothesis that public risk perception is updated periodically when shortage events are experienced. The policy making process module uses an algorithm capturing the hypothesized decision making process to select policy actions (or in-action) from a set of feasible actions in response to the system states tracked by the model and observable to decision makers.

The model was tested and parameterized using mix of quantitative data on water demands, supplies and costs and qualitative data from document analysis and interview data covering 1990 to 2010 period. Given that not only the parameters but also the structure of the public perception and the policy making process sub-systems is contested, a different approach must be taken to assess the robustness of these modules. Presented here is the development of the model, results of model testing against the historic reference modes using Las Vegas as an example, and future work planned to improve the robustness of the model.