Identifying and Planning for Vulnerabilities in the San Bernardino Valley Municipal Water District’s Water Management Plans

This interactive tool presents the results of a study that evaluated the performance of the San Bernardino Valley Municipal Water District (Valley District) water plans—specifically, the 2015 Regional Urban Water Management Plan (RUWMP; Water Systems Consulting, Inc., 2016)—under a wide range of future conditions. Through this study, researchers assessed whether demand for water outstripped the sustainable use of supply sources in the Valley District service area, taking into consideration future changes in climate, drought, and imported water supply and demand factors (e.g., population growth, conservation behavior). The research team examined how planned water supply investments, such as demand-management strategies, and investments in alternative local and imported water supply projects could enhance the robustness of the Valley District’s system across these future changes.1 To do this, the researchers

  1. evaluated water supply and demand across 1,872 plausible futures
  2. defined key future vulnerabilities for the Valley District
  3. characterized whether new local water supply projects and demand-management options reduced future gaps between supply and demand or whether additional measures are needed
  4. quantified uncertainty both in the current water supply system and compared with the Valley District’s Reliability Factor2
  5. identified signposts that indicated when demands might exceed supplies and when management plans might need to be adapted.

This interactive tool is intended to complement and present the results of the study’s technical publication (Miro et al., 2021).

Methods

To carry out these objectives, the research team developed a three-part modeling framework, used it to perform stress tests on the Valley District’s RUWMP demands and supplies against a wide range of future conditions, and then employed system performance criteria to analyze study results. The three-part modeling framework consisted of

  1. a demand model developed in prior work with the Valley District3
  2. a supply model based on water supply estimates in the RUWMP and extended with numerical models of State Water Project (SWP) deliveries and local surface water supplies
  3. an empirical machine learning model of the San Bernardino and Rialto-Colton groundwater basins.

Complete details of these models can be found in the study’s technical publication (Miro et al., 2021).

Once linked together, these models estimated annual water demand, annual water supply availability, and annual water demand by supply source; annual groundwater demand by groundwater basin; and annual changes in groundwater availability from groundwater pumping under 1,872 futures. These 1,872 futures were formed from combinations of four future demand conditions, 12 future projections of changes in precipitation and temperature, four synthetic precipitation time series of future drought conditions, and nine configurations of infrastructure that would affect imported water deliveries from the SWP.4

Under each of these futures, we assessed the performance of the Valley District’s RUWMP with two performance metrics that indicated when the system failed to meet management goals:

  1. demand for groundwater that exceeds sustainable use of groundwater supplies, which is calculated as the difference between annual available water supply, when groundwater use is constrained to Safe Yield values,5 and annual water demand
  2. loss in groundwater availability past a threshold that indicates when low yield areas stop producing water.6

Findings

Key Future Vulnerabilities

Our study found that the Valley District’s current water management plan—the 2015 RUWMP—is vulnerable to futures with long-duration droughts; hot temperatures; high per capita demand and population growth; and low deliveries from the SWP, the Valley District’s primary source of imported surface water, which is delivered from the Sacramento–San Joaquin Delta in northern California (also referred to as the Bay Delta). Figure 1 illustrates the timing and number of futures that lead to excess demand (shown in red). In each year shown in Figure 1, 1,872 squares represent whether there is sufficient supply to meet demand (shown in blue) or whether excess demand occurs (red). Because there are many futures, it is important to consider the full range of their results, as well as their distribution. Figure 1 shows their full range, including minimum and maximum values for each year depicted. The average value of all of the results in each year is also shown in the figure, represented by gray horizontal lines and labeled with the average value.

How to Use the Tool

  • Use the drop-down menus under "Future Water Demand," "Future Drought Conditions," or "Future Climate Changes" to select futures of interest.
  • The median values for the selected futures panel will automatically update with the median values of those futures selected in the drop-down menus.
  • To view the specific conditions for a given value of excess demand on the figure, hover or tap on a square; a tool tip will appear.

Figure 1. Excess Supply for San Bernardino Valley Municipal Water District, 2020–2050

NOTES: Squares represent the excess supply (blue) or excess demand (red) in each year shown for one of the scenarios selected. Gray horizontal bars indicate the median value for each year.

Performance of New Local Water Supply and Demand-Management Options

We also examined the performance of investments in new local water supply projects that focus on artificial groundwater recharge and demand-management strategies in reducing system vulnerabilities. We found that investments in new local water supply projects that enhance the recharge capacity of groundwater basins eliminated the majority of futures in which supplies did not meet demands, suggesting that investments in local supply projects could provide even greater robustness to future conditions than investments in imported supplies (see Miro et al., 2021, for the full analysis). Finally, we found that demand management—specifically, the future water demand conditions with low per capita water use—can significantly reduce vulnerabilities to drought and other climate changes, even in the absence of investments in both imported and local water supplies. Figure 2 shows the results of this analysis for the San Bernardino basin, depicting the remaining usable storage above the threshold of 4,465,000 acre feet (AF) when wells need to be deepened. The top panel shows groundwater availability above (in blue) this threshold (termed usable storage) and below (in red) this threshold under the range of selected futures when new water supply projects are not added. The bottom panel shows the same results when new water supply projects are added.

How to Use the Tool

  • Use the drop-down menus under “Future Water Demand,” “Future Drought Conditions,” or “Future Climate Changes” to select futures of interest.
  • The median values for the selected futures panel will automatically update with the median values of those futures selected in the drop-down menus.
  • To view the specific conditions for a given value of excess demand on the figure, hover or tap on a square; a tool tip will appear.

Figure 2. San Bernardino Basin Remaining Usable Storage, 2020–2050

NOTES: Squares represent the usable storage in each year shown for one of the scenarios selected. Gray horizontal bars indicate the median value for each year.

Valley District Reliability Factor

To account for uncertainties in supply and demand, the RUWMP and Valley District’s other planning efforts employ a Reliability Factor of 10 percent. This Reliability Factor is applied to estimated demands and ensures that supplies are at least 10 percent more than demand projections. By studying the full range of Reliability Factor values that would be needed to cover excess demand to 2050, as shown in Figure 3, we found that the Valley District could consider an adaptable Reliability Factor of 15 percent relative to baseline demands and that this value could be reevaluated each time the RUWMP is updated. Also shown in Figure 3 are those futures in which excess demand occurs above the 15-percent Reliability Factor. To account for these cases and for changes in the gap between supply and demand over time, we also suggest that the Valley District track the following for planning beyond 2040:

  • SWP deliveries below 50 thousand acre-feet (TAF) signal that the Reliability Factor might need to be increased.
  • Total demand at or above 360 TAF signals that the Reliability Factor might need to be increased.
  • As water supply projects, including imported water supply projects (e.g., Sites Reservoir and Delta Conveyance), or the new local water supply projects shown in Figure 2 come online, the Reliability Factor might need to be reassessed and potentially lowered.

How to Use the Tool

  • Use the drop-down menus under “Future Water Demand,” “Future Drought Conditions,” or “Future Climate Changes” to select futures of interest.
  • The median values for the selected futures panel will automatically update with the median values of those futures selected in the drop-down menus.
  • To view the specific conditions for a given Reliability Factor value shown on the figure, hover on a square; a tool tip will appear.

Figure 3. Reliability Factor and Years with Excess Demand, 2020–2050

NOTES: Symbols represent the Reliability Factor need to cover cases with excess demand from Figure 1 (shown as red squares in Figure 1). Reliability Factor is calculated as a percent increase in supply needed to meet demand.

Footnotes

  1. New local water supply projects included in this study are those detailed in the Upper Santa Ana River Habitat Conservation Plan in the San Bernardino and Rialto-Colton groundwater basins. Imported water supply investments consist of Sites Reservoir and Delta Conveyance. Return to content
  2. The Valley District employs a 10-percent Reliability Factor in its 2015 RUWMP to account for uncertainties in supply and demand. The 10-percent Reliability Factor is applied to demand estimates, and supply planning is carried out to ensure that supplies are available at least 10 percent over estimated demands. Return to content
  3. RAND Corporation researchers worked with the Valley District to first explore uncertainties in the demand projections contained within the RUWMP. See Miro et al., 2018. Return to content
  4. These nine configurations of infrastructure and operations in the Sacramento–San Joaquin Delta (also referred to as the Bay Delta) were modeled by the State of California Department of Water Resources using CalSim2 and were provided to the RAND team.Return to content
  5. Safe Yield is an annual volume of groundwater that can be extracted from a groundwater basin without causing undue drawdown of the basin. It is often determined as part of legal agreements that adjudicate groundwater uses within a basin.Return to content
  6. This occurs in the San Bernardino basin when groundwater availability is less than 4,465,000 acre-feet (AF) and in the Rialto-Colton basin when groundwater availability is less than 1,278,000 AF. These values were determined in prior work (Wicks and Yeh, 2020, p. 103). Return to content

References

  • Miro, Michelle E., David G. Groves, David Catt, and Benjamin M. Miller, Estimating Future Water Demand for San Bernardino Valley Municipal Water District, Santa Monica, Calif.: RAND Corporation, WR-1288-SBVMWD, 2018. As of December 13, 2021: https://www.rand.org/pubs/working_papers/WR1288.html
  • Miro, Michelle E., David Groves, Bob Tincher, James Syme, Stephanie Tanverakul, and David Catt, “Adaptive Water Management in the Face of Uncertainty: Integrating Machine Learning, Groundwater Modeling and Robust Decision Making,” Climate Risk Management, Vol. 34, 2021.
  • Water Systems Consulting, Inc., 2015 San Bernardino Valley Regional Urban Water Management Plan, San Luis Obispo, Calif., June 2016. As of December 13, 2021: https://www.sbvmwd.com/home/showdocument?id=4196
  • Wicks, Lauren, and J. Yeh, Usable Groundwater in Storage Estimation for the San Bernardino, Rialto-Colton, Riverside, and Arlington Groundwater Basins—Summary Report, San Dimas, Calif.: Geoscience Support Services, Inc., 2020.

About This Tool

This interactive tool presents the results of a study that evaluated the performance of the San Bernardino Valley Municipal Water District water plans under a range of future conditions, including changes in climate, drought, and water demand. The research described in this tool was sponsored by the San Bernardino Valley Municipal Water District and conducted in the Community Health and Environmental Policy Program within RAND Social and Economic Well-Being.

Community Health and Environmental Policy Program

RAND Social and Economic Well-Being is a division of the RAND Corporation that seeks to actively improve the health and social and economic well-being of populations and communities throughout the world. This research was conducted in the Community Health and Environmental Policy Program within RAND Social and Economic Well-Being. The program focuses on such topics as infrastructure, science and technology, community design, community health promotion, migration and population dynamics, transportation, energy, and climate and the environment, as well as other policy concerns that are influenced by the natural and built environment, technology, and community organizations and institutions that affect well-being. For more information, email chep@rand.org.