Using Robust Decisionmaking as a Tool for Water Resources Planning in Southern California

Kirsten Feifel
Posted on: 4/22/2010 - Updated on: 10/28/2021

Posted by

Kirsten Feifel

Project Summary

Water planners have been struggling to incorporate the impacts of climate change into their planning process due to the inherent uncertainties in regards to the type and magnitude of impacts that will be experienced at the local level. To help water planners incorporate climate change into their long-term plans, the RAND Corporation piloted the Robust Decisionmaking (RDM) tool in the Southern California region in collaboration with the Inland Empire Utilities Agency (IEUA). RDM integrates a variety of climate scenarios, management plans, and costs, and is able to assess vulnerabilities and trade-offs in comparison with other plans. For the IEUA case, results indicate that their long-term water management plan would perform best in light of climate change if it were augmented with near-term water efficiency strategies. In a survey, water planners found the RDM results as a useful way to understand and incorporate the impacts of climate change into long-term planning. RDM has since been applied in other use cases to respond to climate change and other situations associated with high levels of uncertainty such as pandemics and terrorism.


Traditionally, water planners have used historical streamflow data and weather patterns to infer seasonal water forecasts. However, climate change is expected to change weather patterns, air temperature, and precipitation patterns in an as yet relatively unpredictable fashion at the local scale. Water managers are seeking methods to incorporate the impacts of climate change into their current planning processes but are hampered by the uncertainty in future climate forecasts. In general, climate change impacts of concern relative to water resources include warmer temperatures, reduced precipitation, reduced snowpack, shifts in peak spring flow, and higher consumer demands. The extent and magnitude of these impacts will vary from region to region. Climate change is making it hard to plan for the future; it has become clear to most utility managers that past weather and hydrologic records will no longer provide an accurate guide to future weather and hydrology.

While many water and wastewater utilities recognize the potential impacts of climate change, there has been a missing link between recognition and the transition to action. This is due in part to the relatively high degree of uncertainty inherent in downscaled global climate models. It has generally been assumed that it is difficult for planners to accurately plan for the future without precise ranges of future climatic variability.

In 2006, the RAND Corporation was awarded a multi-year National Science Foundation grant to develop and evaluate new analytical methods to incorporate uncertainty about climate change into water resource decisions. To complete its study, RAND selected to partner with IEUA, a water and wastewater utility based in Riverside, California, as its model case study.

IEUA is a municipal water agency that delivers supplemental imported and recycled water resources to an area of 242 square miles in the southwestern corner of San Bernardino County with a population of 800,000 and growing. IEUA operates five water recycling facilities and processes an average of 60 million gallons of wastewater per day. In 2005, IEUA released its Regional Urban Water Management Plan (UWMP), a forward-looking and planning document for the utility. The UWMP anticipates a population increase of about 800,000 to 1.2 million people by 2030 and outlines a plan to meet future water demands by improving water-use efficiency and developing local resources. For the study, the RAND Corporation worked in collaboration with IEUA to assess the efficacy of the UWMP in relation to future climate scenarios and then developed alternative management strategies available to IEUA to help combat the effects of climate change. 


To complete this project, the RAND Corporation utilized multiple technological tools, including the Water Evaluation and Planning (WEAP) system, downscaled climate models, and the RDM tool. WEAP, developed by the Stockholm Environment Institute, integrates physical hydrologic processes with consumer demands and infrastructure. WEAP was used to evaluate the effectiveness a variety of water management plans would have under different climate scenarios. The National Center for Atmospheric Research developed future climate scenarios for the project using the results of 21 atmosphere-ocean general circulation models downscaled to the Southern California region. Results indicate the climate in Southern California could range from 0.1-2.1°C warmer and there could be a -19 to +8% change in wintertime precipitation. These results were transformed into different climate scenarios. Finally, the RAND Corporation developed RDM, a new decision analysis methodology designed to support decision-making under uncertain conditions. RDM evaluates the performance of different management plans under a variety of scenarios, identifies vulnerabilities within management plans, and finally identifies the most robust management plans to vulnerabilities and presents key tradeoffs within various plans. To evaluate the efficacy and usefulness of the RDM tool, the RAND Corporation presented the study results in four workshops to water resource managers. Participants were surveyed before and after each workshop to evaluate the water resource managers’ perceptions of the RDM tool and its conclusions. The survey was designed to discern whether or not water managers felt more empowered to properly plan for the effects of climate change once they were presented the results from the RDM tool.

Ultimately, the RAND Corporation presented two types of results at its workshops. The first workshop presented an evaluation of the IEUA UWMP under four climate scenarios. Findings generally indicated that if the impacts of climate change are minimal, the UWMP will meet its supply goals for 2030. However, if climate change causes significant warming and drying trends, the UWMP could perform poorly and miss many of its goals, causing economic losses. Surveys indicated that resource managers did not infer enough meaningful information from these results to develop alternative management plans that incorporate the impacts of climate change. The following three workshops presented an RDM analysis in which the UWMP was evaluated against a much larger set of scenarios with different assumptions regarding the extent of climate change, management plan, and costs; in sum, over 200 scenarios were run under the RDM analysis. Under this analysis, cost was 20% greater than expected costs in 120 of the 200 scenarios. They found that the UWMP was particularly vulnerable to future conditions that were drier with reduced access to imported water and when natural percolation of the groundwater basin decreased. Eight additional management strategies beyond the UWMP were analyzed to assess their ability to reduce vulnerabilities under a wide variety of climate scenarios. Strategies varied from increasing water use efficiency, recycling stormwater for groundwater replenishment, and developing the region’s water recycling program. In all cases, augmenting the UWMP with additional management strategies led to lower costs and reduced vulnerability.

Under the RDM analysis, the best management plan was adaptive and included near-term implementation of more water-use efficiency techniques. When water managers were presented with these results, surveys indicated that this type of information caused them to increase the belief that they could adequately plan for the effects of climate change despite the uncertainty in forecasts.

Outcomes and Conclusions

Based upon the analysis and survey results, the RAND Corporation concluded that to help water resource managers prepare for climate change, scenarios should be analyzed using as many plausible future climate conditions and management strategies as possible. The RDM tool helps to interpret and quantify the significance of the results into meaningful terms. It was concluded that local solutions should not be overlooked when developing solutions to the impacts of climate change. Local policies and management opportunities may be more cost-effective, reliable, and feasible when compared to other options.

Since the RDM tool was piloted with IEUA, the RAND Corporation has used it to support climate-informed decision-making for water resources in Monterrey (Mexico) and Lima (Peru), conservation planning for the northern pygmy salamander, and coastal restoration and planning in Louisiana.


Feifel, K. (2020). Using Robust Decisionmaking as a Tool for Water Resources Planning in Southern California [Case study on a project of the RAND Corporation]. Version 2.0. Product of EcoAdapt’s State of Adaptation Program. (Last updated July 2020)

Project Contacts

Affiliated Organizations

The RAND Corporation is a nonprofit institution that helps improve policy and decisionmaking through research and analysis. RAND focuses on the issues that matter most such as health, education, national security, international affairs, law and business, the environment, and more. With a research staff consisting of some of the world's preeminent minds, RAND has been expanding the boundaries of human knowledge for more than 60 years. As a nonpartisan organization, RAND is widely respected for operating independent of political and commercial pressures.

Inland Empire Utilities Agency originally named the Chino Basin Municipal Water District (CBMWD), was formed in 1950 to supply supplemental water to the region. Since its formation, the Agency has expanded its areas of responsibility from a supplemental water supplier to a regional wastewater treatment agency with domestic and industrial disposal systems and energy recovery/production facilities.

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