In most U.S. regions, water resources managers and planners will encounter new risks, vulnerabilities, and opportunities that may not be properly managed within existing practices.

This finding is from chapter 3 of Climate Change Impacts in the United States: The Third National Climate Assessment.

Process for developing key messages: The chapter author team engaged in multiple technical discussions via teleconferences from March – June 2012. These discussions followed a thorough review of the literature, which included an inter-agency prepared foundational document,50d47cc1-5a16-4f5c-bb08-bf6f475a5bb8 over 500 technical inputs provided by the public, as well as other published literature. The author team met in Seattle, Washington, in May, 2012 for expert deliberation of draft key messages by the authors wherein each message was defended before the entire author team before this key message was selected for inclusion in the Chapter. These discussions were supported by targeted consultation with additional experts by the lead author of each message, and they were based on criteria that help define “key vulnerabilities.” Key messages were further refined following input from the NCADAC report integration team and authors of Ch. 2: Our Changing Climate.

Description of evidence base: The key message and supporting chapter text summarizes extensive evidence documented in the inter-agency prepared foundational document,50d47cc1-5a16-4f5c-bb08-bf6f475a5bb8 other chapters of the NCA, and over 500 technical inputs on a wide range of topics that were received as part of the Federal Register Notice solicitation for public input. Observed and Projected Trends: Many U.S. regions are facing critical water management and planning challenges. Recent assessments illustrate water management challenges facing California,e610dc47-1231-4cbf-b43d-083cc76aa885 412047fe-33cf-49b8-b714-f1a7b096cd43 4db2c787-a754-422a-8714-80bbb44def23 2b2ce56f-645c-4807-9a16-4460433f4861 32f16a0a-8d25-4e52-9804-1f18632491d6 the Southwest,d9b704d3-1441-4cf8-a7dc-cc2b1d14c8c5 9cb51164-e933-48c9-9265-f09b4a9b63a3 Southeast (Ch. 17: Southeast),d0797088-3f92-4cfc-be8d-15027a28378e 47f6b2ff-a48f-4b48-899d-a901424bf5b2 Northwest,c3b1c82e-1821-465f-8466-9d42799340ad 4babef84-d85e-488e-b8c5-3fb080ebfcd3 43f67f10-aff3-4d61-8d87-a883adb24771 Great Plains,1e9e830a-b4e4-4a40-8390-5013027453d8 and Great Lakes.125c3ecf-fc2d-46dc-b42b-1d41cfb3ec46 The Sacramento-San Joaquin Bay Delta is already threatened by flooding, seawater intrusion, and changing needs for environmental, municipal, and agricultural water uses. Managing these risks and uses requires re-assessment of a very complex system of water rights, levees, stakeholder consensus processes, reservoir system operations, and significant investments, all of which are subject to large uncertainties.7ef83121-d51c-4bc5-b499-e00733fae338 afffeea6-ab1c-4ffa-9667-5174239693f3 4acc879e-eae3-4e14-96d5-5e083a548c50 Given the projected climate changes in the Sacramento-San Joaquin Bay Delta, adherence to historical management and planning practices may not be a long-term viable option,412047fe-33cf-49b8-b714-f1a7b096cd43 4db2c787-a754-422a-8714-80bbb44def23 but the supporting science is not yet fully actionable,c52f2539-9c5e-4ead-b8b7-f1884c5d662e and a flexible legal and policy framework embracing change and uncertainty is lacking. The Apalachicola-Chattahoochee-Flint (ACF) River basin in Georgia, Alabama, and Florida supports a wide range of water uses and the regional economy, creating challenging water sharing tradeoffs for the basin stakeholders. Climate change presents new stresses and uncertainties.47f6b2ff-a48f-4b48-899d-a901424bf5b2 ACF stakeholders are working to develop a management plan that balances economic, ecological, and social values.19d37361-7f68-4f49-a5d9-37d027933146

New information and remaining uncertainties: Changes in climate, water demand, land use, and demography combine to challenge water management in unprecedented ways. This is happening with a very high degree of certainty in most U.S. regions. Regardless of its underlying causes, climate change poses difficult challenges for water management because it invalidates stationarity – the perception that climate varies around a predictable mean based on the experience of the last century – and increases hydrologic variability and uncertainty. These conditions suggest that past management practices will become increasingly ineffective and that water management can benefit by the adoption of iterative, risk-based, and adaptive approaches.

Assessment of confidence based on evidence: The water resources literature is unanimous that water management should rely less on historical practices and responses and more on robust, risk-based, and adaptive decision approaches. Therefore confidence is very high that in most U.S. regions, water resources managers and planners will face new risks, vulnerabilities, and opportunities that may not be properly managed with existing practices.

References :

• A Scientific Assessment of Alternatives for Reducing Water Management Effects on Threatened and Endangered Fishes in California's Bay Delta (7ef83121)
• Water Resources Sector Technical Input Report in Support of the U.S. Global Change Research Program, National Climate Assessment - 2013 (50d47cc1)
• A Review of the Use of Science and Adaptive Management in California's Draft Bay Delta Conservation Plan (afffeea6)
• Sustainable water deliveries from the Colorado River in a changing climate (9cb51164)
• webpage A Grass-roots Stakeholder Organization for the ACF River Basin (19d37361)
• Climate Variability and Change Assessment for the ACF River Basin, Southeast US. Georgia Water Resources Institute (GWRI) Technical Report sponsored by NOAA, USGS, and Georgia EPD (47f6b2ff)
• Value of adaptive water resources management in northern California under climatic variability and change: Dynamic hydroclimatology (412047fe)
• Adapting California’s water system to warm vs. dry climates (e610dc47)
• Climate change impacts on water management and irrigated agriculture in the Yakima River Basin, Washington, USA (4babef84)
• Mitigating the Effects of Climate Change on the Water Resources of the Columbia River Basin (c3b1c82e)
• Lake Superior Regulation: Addressing Uncertainty in Upper Great Lakes Water Levels. Final Report to the International Joint Commission. March 2012 (125c3ecf)
• Basin-scale water system operations with uncertain future climate conditions: Methodology and case studies (32f16a0a)
• Assessing reservoir operations risk under climate change (4db2c787)
• Climate change and its implications for water resources management in south Florida (d0797088)
• Climate change impacts on water management in the Puget Sound region, Washington State, USA (43f67f10)
• Sustainable Water and Environmental Management in the California Bay-Delta (4acc879e)
• Integrated Forecast and Reservoir Management (INFORM) for Northern California: System Development and Initial Demonstration. CEC-500-2006-109 (2b2ce56f)
• CLIMATE CHANGE: Stationarity Is Dead: Whither Water Management? (c52f2539)
• Water supply risk on the Colorado River: Can management mitigate? (d9b704d3)
• Doomed reservoirs in Kansas, USA? Climate change and groundwater mining on the Great Plains lead to unsustainable surface water storage (1e9e830a)