The time is now for risk-based water supply planning
February 26, 2020
Few cheap or easy solutions remain for water supply in the US. Integrated water resources planning is a first step to understanding your risks
¡°Embrace uncertainty.¡± ¡°Look beyond your headlights.¡± ¡°Don¡¯t plan to the edge, allow for redundancy.¡± ¡°Regularly assess and question your assumptions.¡± This is some of the advice our team heard from large-scale water providers across the US regarding integrated water supply planning as we??on this topic for the Water Research Foundation.
Taking a long-range look at our water supply is more important now than ever before. The US population is growing, predominantly and most rapidly in areas that are already considered water stressed. For example, 12 of the 15 fastest-growing cities in the US are in semi-arid or arid regions of the Western US, largely Texas and the Southwest. In addition, the climate is changing. While water conservation and efficient water use are powerful tools for reducing per capita water demand in many communities, these measures cannot address all needs.?
The US population is growing, predominantly and most rapidly in areas that are already considered water stressed.
The times they are a changin¡¯
According to the recent??from the US Global Change Research Program, ¡°significant changes in water quantity and quality are evident across the country. These changes, which are expected to persist, present an ongoing risk to coupled human and natural systems and related ecosystem services.¡±
Historical baseline climate conditions are typically factored into water supply system design and operations. Climate change is likely to induce significant deviations from historical baseline conditions, including the frequency and intensity of extreme events. Large-scale global changes ultimately have regional and local effects, as reflected in continuing changes to patterns of temperature, precipitation, and extreme event occurrence. These changes directly impact water resources. We will likely see altered streamflow regimes, new temperature patterns, enhanced reservoir evaporation, and changing water-quality conditions.
A changing climate means previous assumptions of stationarity¡ªa reliance on historical baseline conditions for design and operations and planning for future needs¡ªare no longer valid due to large-scale shifts in climate conditions and the sometimes-accelerating rates of change for key parameters. It is now important to understand and quantify the risks associated with changing climate conditions in order to develop solutions that provide sustainable and consistent access to water resources.
In addition, new regulations to address groundwater sustainability, water quality, and species protections pose significant threats to the water supply reliability of existing systems, further underscoring the importance for integrated planning of future water supplies.
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The peak of the 2011 drought in the Southern Great Plains and Southwest. At peak, 97% of Texas was in extreme or exceptional drought. (Map courtesy of the National Drought Mitigation Center)
Water, water everywhere?
Traditional water management and planning often does not address risks that change over time. For years, it has been common to apply static assumptions about future demands and supplies, future conditions, and system performance. The key drivers of climate variability, population and economic growth, other internal and external motivating factors, and recent and possible future technological developments, collectively challenge traditional approaches to water supply planning.
Where will our ¡°new¡± water come from? What role will inland brackish water and coastal seawater desalination play? How much of our water can be reused, how often, and for what purposes? Will new on-channel dams be part of the water supply portfolio mix; can water be stored off-channel or underground in aquifers?
The answer to each of these questions is, of course, ¡°it depends.¡± It depends on future water supply availability, future water demands, technological capabilities, environmental and regulatory considerations, and costs.
Our most important challenge in the 21st century is ensuring reliable water to meet diverse needs under uncertain conditions.
In the US and much of the developed world, delivering clean potable water and effectively removing wastewater were the main urban infrastructure accomplishments of the 20th century. Our most important challenge in the 21st century is ensuring reliable water to meet diverse needs under uncertain conditions.
So, what is the best approach for this brave new world of water management? Fortunately, there is a proven framework: integrated water resources planning.
Risk, like beauty, is in the eye of the beholder
Across the country, many forward-thinking communities and water providers are evolving their water resources planning and management approaches to incorporate uncertainty around key risks. Our Â鶹´«Ã½ team has been fortunate to support many of these communities, from California to Colorado and Texas to Oregon, from small municipal utilities to large, basin-wide wholesale water providers.
Risk-based approaches are replacing a traditionally narrow focus on benefit-cost analysis or firm yield. When a risk-based approach is done right, it builds on a solid foundation of credible data, defensible modeling, and transparent decision-making. This approach also incorporates input and buy-in from stakeholders along the way. Key performance indicators are developed and assessed for system reliability, resilience, vulnerability, and sustainability, often over a planning horizon of 50 to 100 years. Water supply needs are balanced with other objectives, such as recreation, navigation, hydropower production, flood protection, ecosystem health, or water quality.
Although risk-based water supply evaluations can be more complex to communicate, they can help identify synergy between or competition among potential water management strategies. They can also reveal ¡°what if¡± pathways that allow for changing conditions and enhance stakeholder engagement in determining shared values.
In many regions, water supply reliability is decreasing due to factors such as climate change or increased regulations.
The future isn¡¯t what it used to be
In many regions of the US, the low-hanging fruit for water supply has been picked and no cheap or easy solutions remain. Increasingly, our shared water future includes more diverse portfolios of structural and non-structural solutions, changes in water policy and drought management, enhanced water conservation and water use efficiency, and expanded direct and indirect potable and non-potable reuse.
Our water planning future must evolve to incorporate plausible future climate conditions that are wider in range than those in recorded history. We also must adapt to changing societal values and socioeconomic goals.
Most investors have heard that ¡°past performance is no indication of future results.¡± This is also true with ensuring a safe, reliable water supply for people, industry, and the environment. What level of risk can we tolerate? And what are we going to do¡ªand how much are we willing to pay¡ªto mitigate or manage that risk? While we don¡¯t have all the answers, we do know that the proven framework of integrated water resources planning is a first step to understanding the range and severity of your risks so that your investments can be prioritized accordingly.
About the authors
Eric Hersh?is a water resources engineer based in Austin, Texas.?Eric¡¯s Â鶹´«Ã½ includes a focus on hydrology, geospatial technology, hydro-informatics, environmental flows, GIS, and sustainability.?
Ryan Murdock?is our water resources leader in Texas, working from Austin.?Ryan has 20 years of experience in comprehensive planning for strategic, large-scale water resources infrastructure and operations programs.?
