finding 3.3 : key-message-3-3

Water management strategies designed in view of an evolving future we can only partially anticipate will help prepare the Nation for water- and climate-related risks of the future (medium confidence). Current water management and planning principles typically do not address risk that changes over time, leaving society exposed to more risk than anticipated (medium confidence). While there are examples of promising approaches to manage climate risk, the gap between research and implementation, especially in view of regulatory and institutional constraints, remains a challenge.

This finding is from chapter 3 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

Chapter authors were selected based on criteria, agreed on by the chapter lead and coordinating lead authors, that included a primary expertise in water sciences and management, knowledge of climate science and assessment of climate change impacts on water resources, and knowledge of climate change adaptation theory and practice in the water sector.

The chapter was developed through technical discussions and expert deliberation among chapter authors, federal coordinating lead authors, and staff from the U.S. Global Change Research Program (USGCRP). Future climate change impacts on hydrology, floods, and drought for the United States have been discussed in the Third National Climate Assessment3ff0e30a-c5ee-4ed9-8034-288be428125b and in the USGCRP’s Climate Science Special Report.e8089a19-413e-4bc5-8c4a-7610399e268c,a29b612b-8c28-4c93-9c18-19314babce89 Accordingly, emphasis here is on vulnerability and the risk to water infrastructure and management presented by climate variability and change, including interactions with existing patterns of water use and development and other factors affecting climate risk. The scope of the chapter is limited to inland freshwater systems; ocean and coastal systems are discussed in their respective chapters in this report.

Description of evidence base:

There is wide documentation in the scientific literature that water management practice and engineering design use the observed historical record as a guide to future expectations. This implies that significant departures from those expectations would pose greater-than-anticipated risks, and scenario analyses have demonstrated this to be the case, particularly in studies of large water supply systems. In particular, the Climate Science Special Report75cf1c0b-cc62-4ca4-96a7-082afdfe2ab1 notes the potential for increased clustering (for example, heat waves and drought) or sequences of extremes and rapid transitions in climate. There is a growing literature that documents the use of robustness-based planning approaches, especially for water supply planning but also for coastal planning. These approaches provide promising methodologies for addressing climate change in water planning, although their complexity and cost—and limited planning resources—may be impediments to wide-scale adoption.

The literature also provides examples of some more innovative approaches applied to managing risks in an adaptive manner, including updating reservoir operations,1cad6d5a-ed6a-4fa7-9f31-fcb196b570de,a0605c2c-bdc2-4018-904b-e5a274b7de3c,e005a91f-ca69-4b4c-8586-2a2e4d346e09 employing financial instruments for risk transfer or financial risk management,0a7da6ff-becc-4a36-9dc0-8c31a0731d82,fe55773f-7d75-464d-83c2-29950b592f52 and the use of adaptive management.a7f7d233-62b8-4c4e-ac66-706a9f9389a0 However, the lack of broader-scale adoption and wider demonstration prevents more conclusive statements regarding the general utility of these approaches at this time.3e71b7af-869b-4adb-a93c-bed6640761f5

New information and remaining uncertainties:

The key uncertainty in assessing the current state of preparation of the Nation’s water infrastructure and management for climate change is the lack of public data collected about key performance and risk parameters. This includes the state of water infrastructure, including dams, levees, distribution systems, storm water collection, and water and wastewater treatment systems. For some of these systems, current performance information may be available, but there is little knowledge of what future performance limitations may be. Furthermore, much of this information is not publicly available, although it may be collected by the many local and state agencies that operate these infrastructure systems. A large number of case studies have illustrated that observed and projected changes in climate could place systems at risk in ways that exceed current expectations.

Assessment of confidence based on evidence:

The Key Message is stated with medium confidence due to the limited assessment that has been performed on water infrastructure systems and management regimes, and due to the nascent and limited assessment of proposed adaptive responses.

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