Residents in the mountain-west region of the US consistently rank at the top of water users (measured by per capita residential use)[1]. Major population centers in the Utah Lake and Jordan River Basins are no exception, and the majority of residential water use goes towards outdoor watering [2]. For comparison, the national average of outdoor residential water use is about 30% of total use [3]. Urban water demands and availability are subject to changes in:
 

• Climate conditions
• Growth and development patterns
• Behavior, perception, and public understanding of water-related issues

Systems models that incorporate multiple drivers of change, uncertainty, and system complexities can be used to address water availability, management, and planning challenges.
 

Research Objectives and Questions

Modeling Workflow and Results

A 10-year moving average of the Standardized Precipitation-Evapotranspiration Index (SPEI) [4] was used to forecast climate conditions. The data extends from 1950-2099 based on CCSM4 MACA Downscaled Climate Data [5-6] for Utah Lake (Provo) and Jordan River (SLC) Basins. Over the next 80 years, there is a significant drop in SPEI which reflects generally hotter/drier conditions (refer to Figure 1).

Figure 1 - 10-yr moving average SPEI

  Urban land use change was incorporated in the model assuming “Business as Usual” development practices. Future development was simulated using a Real Estate Market Model (REMM) [7], and outputs were post-processed by researchers in the University of Utah Department of City and Metropolitan Planning (refer to Figure 2).

Figure 2 - Land use Change 2005-2040

A GoldSim model of the Utah Lake and Jordan River basins was used to represent water deliveries from water supply sources to users (residents, institutions, irrigation), and then their various endpoints (wastewater treatment plants and receiving waters). This modeling platform incorporates inherent uncertainties through Monte Carlo simulations (e.g. allowing variability in daily per capita water use) and is useful for representing complex interactions and feedback between subsystems. A screen capture of part of the GoldSim model is shown in Figure 3.

Figure 3 - System Model

Key Findings

Strategic development, conservation, and planning are essential for dealing with changing residential outdoor water use and urban water systems.

• There are various drivers of change in future residential water use, some of which have clear compounding effects. Strategic planning (e.g. where to focus time and financial resources) requires an understanding of the relative contribution of each of these drivers.
• Exploring water use through a probabilistic model helps address uncertainties inherent with human behavior and multiple scenarios allow for exploration of different drivers of change.

 

Future Research Opportunities

Residential outdoor water use is only one part of a complex water system. Changes in this part of the system need to be linked to other parts of the system (including surface and groundwater sources, and downstream receiving waters). In this particular system, there are several multi-purpose reservoirs, and any changes in demands will have cascading effects outside of residential water use sector (e.g. energy generation, flood control operations). There are also many opportunities to explore mechanisms of change (e.g. lawn irrigation technologies). Additionally, the modeling framework and many of the data sources presented here are widely applicable and available for other urban water systems in the western United States.
 

Acknowledgements

This article was developed under assistance agreement number 835866-01 awarded by the US Environmental Protection Agency to Dr. Michael Barber. It has not been formally reviewed by EPA. The views expressed in this document are solely those of the authors and do not necessarily reflect those of the agency. EPA does not endorse any products or commercial services mentioned in this publication. Special thanks to Debolina Banerjee from the Department of City and Metropolitan Planning at the University of Utah for processing REMM model data.

Contributors:
Carly Hansen, PhD (with Oak Ridge National Laboratory – Environmental Sciences Division, hansench@ornl.gov)
Steve Burian, PhD (with University of Utah – Civil and Environmental Engineering and the U Water Center)

This model was presented at the 2019 American Water Resources Association Conference in November 2019 as part of the poster showcase. To view the entire poster presentation, click here.
 

References