Focus Areas Click a focus area below to expand Understanding Climate Modeling and Uncertainty Proceedings of the Water Utility Climate Alliance Piloting Utility Modeling Applications (PUMA) Workshop (2010) CMIP6 FAQ for Water Managers (2025) The Influence of Downscaling on Climate Projections (2024) Improving the Vegetation Representation in Hydrologic Models Alters Hydroclimate Projections (2023) Scaling and Application of Climate Projections to Stormwater and Wastewater Resilience Planning (2022) Co-Producing Actionable Science for Water Utilities (2016) Understanding Climate Risks Planning for Adaptation and Resilience Implementing Climate Projects Training Water Utilities for Climate Readiness Developing Additional Resources and Presentations

Climate-resilient water utilities are an essential part of strong communities. WUCA strives to advance water utility climate adaptation so that communities can thrive in a changing world Collaboratively advancing water utility climate change adaptation Mission Climate-resilient water utilities supporting thriving communities Vision Contact Us Latest reports from WUCA Help your utility prepare for climate change Warming is here and now. Climate adaptation planning is not just about the future. Water utilities are experiencing the effects of a changing climate on their water resources today. Know your system and explore its vulnerabilities. Assess your water system to identify vulnerabilities. Risks can only be reduced if they are identified. Plan for multiple futures. Predicting the future is not feasible but anticipating plausible warmer future climates is. Prepare to face a variety of scenarios. Capacity building and assessment are part of the adaptation equation. Developing the technical and managerial expertise to identify and assess climate risks to a system is as much a part of adaptation as the steps taken to implement risk reduction measures. Sign up for email updates We'll keep you in the loop about upcoming webinars, case studies, and opportunities to participate Name Organization Email Sign Me Up Thanks for submitting! We'll be in touch.

Climate change is affecting the water sector by altering the water cycle and weather patterns. Extreme events such as droughts, heatwaves, floods, hurricanes, and wildfires are increasing in severity and frequency, posing critical risks to drinking water, wastewater, and stormwater utilities. The Water Utility Climate Alliance (WUCA) advances climate change adaptation, planning, and decision-making to ensure that water utilities, and the communities they serve, can thrive in the face of these emerging challenges.  WUCA leverages collective utility experiences to develop leading practices in climate change adaptation and mitigation that are actionable, equitable, and serve as a model for others.We collaborate, with each other and our partners, to enable water utilities to respond to climate change impacts on utility functions and operations to protect our water systems today and into the future. 2025 Work Plan 2025 Annual Report 2022-2026 Strategic Plan Member Utilities Austin Water Central Arizona Project Denver Water El Paso Water Massachusetts Water Resources Authority Metropolitan Water District of Southern California New York City Department of Environmental Protection Philadelphia Water Department Portland Water Bureau San Diego County Water Authority San Francisco Public Utilities Commission Seattle Public Utilities Southern Nevada Water Authority Tampa Bay Water Leadership Executive Chair: Alan Salazar, Denver Water Executive Vice-Chair: Andrew Lee, Seattle Public Utilities Staff Chair: Taylor Winchell, Denver Water Staff Vice Chair: Ann Grodnik-Nagle Seattle Public Utilities History In January 2007, the San Francisco Public Utilities Commission hosted the first national Water Utility Climate Change Summit, which was attended by more than 200 water and wastewater utility executives, government officials, climate change experts and environmental leaders. The purpose of the gathering was to help participants better understand the impacts of climate change on water-related infrastructure and water resource supplies. Shortly after the summit, the Water Utility Climate Alliance (WUCA) was formed to provide leadership and collaboration on climate change issues affecting the country's water agencies. Today, the organization comprises 14 of the nation's largest water providers. WUCA members supply drinking water for more than 50 million people throughout the United States.

WUCA Resource Library Search Search the website instead Please report broken links via our contact form WUCA Annual Reports Water Utility Climate Alliance Annual Report 2025 Water Utility Climate Alliance Annual Report 2024 Water Utility Climate Alliance Annual Report 2023 Water Utility Climate Alliance Annual Report 2022 Water Utility Climate Alliance Annual Report 2020 Water Utility Climate Alliance Annual Report 2019 Water Utility Climate Alliance Annual Report 2018 Water Utility Climate Alliance Annual Report 2017 WUCA Strategic Plans Water Utility Climate Alliance Strategic Plan 2022-2026 Water Utility Climate Alliance Strategic Plan 2017-2021 Water Utility Climate Alliance Strategic Plan 2012-2016 WUCA Guidance Documents How Do North American Water Agencies Define Water Supply Level of Service, 2025 CMIP6 Frequently Asked Questions: A resource for water managers, 2024 Improving the Vegetation Representation in Hydrologic Models Alters Hydroclimate Projections, A Summary of Impacts in Several Western U.S Basins, 2024 A Summary of Impacts in Several Western U.S Basins Beyond Barriers to Implementation, A Water Sector Perspective on Sea Level Rise Adaptation, 2022 Scaling and Application of Climate Projections to Stormwater and Wastewater Resilience Planning, 2022 An Enhanced Climate-Related Risks and Opportunities Framework and Guidebook for Water Utilities Preparing for a Changing Climate, Project 5056, 2021 Mapping Climate Exposure and Climate Information Needs to Water Utility Business Functions (project 4729), Executive Summary, 2020 Mapping Climate Exposure and Climate Information Needs to Water Utility Business Functions (project 4729), Research Report, 2020 Water Utility Business Risk and Opportunity Framework A Guidebook for Water Utility Business Function Leaders in a Changing Climate, Project 4729, 2020 Insurance, Bond Ratings and Climate Risk - A Primer for Water Utilities (2019) Co-Producing Actionable Science for Water Utilities, 2016 Research Documents Planning for Sea Level Rise: An AGU Talk in the Form of a Co-Production Experiment Exploring Recent Science,2017 Presentations Presentation materials from all WUCA Resilience Trainings, 2018- present Water system resilience in an uncertain climate future, Presentation at AWWA Sustainable Water Management Conference, Portland, Oregon, 2018 Climate Change Resiliency Planning For Water, Wastewater, and Stormwater, Presentation at AWWA Sustainable Water Management Conference, Portland, Oregon, 2018 Successful Coproduction and Collaboration, Presentation at AWWA Sustainable Water Management Conference, Denver, Colorado, 2018 WUCA Leading Practices Water Utility Climate Alliance Leading Practices Report 2021 Water Utility Climate Alliance Leading Practices Worksheet 2021 Water Utility Climate Alliance Leading Practices Overview 2021 Heat Impacts Case Studies Heat Impacts Case Study, Southern Nevada Water Authority, Nevada Heat Impacts Case Study, Portland Water Bureau, Oregon Heat Impacts Case Study, Oklahoma City Utilities Department, Oklahoma Heat Impacts Case Study, Miami, Florida Equitable Climate Solutions Case Studies Equitable Climate Solutions Case Study, Leveraging Data for Equitable Climate Outcomes Equitable Climate Solutions Case Study, Equity and Affordability in Water Conservation Equitable Climate Solutions Case Study, Equitable Community Engagement for Climate Action Climate Risk Disclosure for Equitable Climate Action, 2025 Climate Investments that Support Underserved Communities, 2025 Engineering Case Studies Engineering Case Study, Tarrant Regional Water District, Pump Station Cooling Solutions, Extreme Heat Adaptation, Dallas/Fort Worth, Texas Engineering Case Study, Seattle Public Utilities & King County, Ship Canal Water Quality Project, Seattle, Washington Engineering Case Study, Southern Nevada Water Authority, Low Lake Level Pumping Station, Drought Adaptation, Las Vegas, Nevada Engineering Case Study, City and County of San Francisco, Sea Level Rise Capital Planning and Guidance, California Engineering Case Study, Miami-Dade Water & Sewer Department, Wastewater Treatment Plant Upgrades for Sea Level Rise and Storm Surge, Florida Engineering Case Study, Copenhagen Cloudburst Management Plan for Extreme Rainfall, Denmark Engineering Case Study, Colorado Dept of Natural Resources Dam Safety Design for Extreme Rainfall, Colorado Engineering Case Study, New York City Dept of Environmental Protection Climate Resilience Standard Operating Procedure for Sea Level Rise and Extreme Weather Events, New York Greenhouse Gas Case Studies Greenhouse Gas Case Study: The Water Energy Nexus (WEN) protocol, California Department of Water Resources, California Greenhouse Gas Case Study: Sustainable Water Treatment Plant, Denver Water, Colorado Greenhouse Gas Case Study: Pumping efficiencies, MWRA, Massachusetts Greenhouse Gas Case Study: Biogas to Local Natural Gas, NYC DEP, New York Greenhouse Gas Case Study: Inline Micro-Hydro, Portland Water Bureau, Oregon Greenhouse Gas Case Study: Energy Recovery System for the Carlsbad Seawater Desalination Plant, Poseidon Water, California Greenhouse Gas Case Study: Pumping Optimization, City of Lakewood, California Greenhouse Gas Case Study: Solar Panels, San Diego County Water Authority, California Greenhouse Gas Case Study: Wind power, solar, and battery storage, Inland Empire Utilities Agency, California Greenhouse Gas Case Study: Carbon Free Water, Sonoma Water, California Greenhouse Gas Case Study: Floating Solar, Lake County Special District, California Greenhouse Gas Case Study: Reducing Fleet Emissions, East Bay Municipal Utility District, California Greenhouse Gas Case Study: Smart Building Cooling, Waternet Amsterdam, Netherlands

WUCA develops research, reports, and trainings to help water and wastewater utilities to understand climate modeling and uncertainty, understand climate risks, plan for enhanced resilience, implement climate solutions, and build internal capacity. In addition to the focus areas outlined below, WUCA also has separate pages dedicated to: Resilience Trainings Leading Practices Climate Modeling with CMIP 6 Understanding Climate Modeling and Uncertainty CMIP6 FAQ for Water Managers (2025) The Influence of Downscaling on Climate Projections (2024) Improving the Vegetation Representation in Hydrologic Models Alters Hydroclimate Projections (2023) Scaling and Application of Climate Projections to Stormwater and Wastewater Resilience Planning (2022) Co-Producing Actionable Science for Water Utilities (2016) Proceedings of the Water Utility Climate Alliance Piloting Utility Modeling Applications (PUMA) Workshop (2010) Understanding Climate Risks It's Hot, and Getting Hotter: Implications of Extreme Heat on Water Utility Staff and Infrastructure, and Ideas for Adapting (2022) Mapping Climate Exposure and Climate Information Needs to Water Utility Business Functions (2021) Executive Summary, Research Report , Appendix, Framework Guidebook , Spectrum Enhanced Climate Related Risk and Opportunities Framework and Guidebook (2021) and Webcast Insurance, Bond Ratings and Climate Risk - A Primer for Water Utilities (2019) Adaptation and Resilience Planning Defining Levels of Service (2025) Representing Climate Change Impacts in Water Demand Modeling (2022) Embracing Uncertainty: A Case Study Examination of How Climate Change is Shifting Water Utility Planning (2015) Decision support planning methods: Incorporating climate change uncertainties into water planning (2010) Implementation Case Studies in Engineering, Mitigation, Stormwater and Wastewater, and Equitable Implementation Leading Practices in Climate Adaptation Beyond Barriers to Implementation -A Water Sector Perspective on Sea Level Rise Adaptation Leading Practices in Climate Adaptation (2021) Climate Risks to Water Utility Built Assets and Infrastructure (2015) Training and Presentations WUCA Adaptation and Resilience Trainings, multiple years Helping Small- and Medium-Sized Water Utilities Plan and Design for A Changing Climate Water system resilience in an uncertain climate future, 2018 Climate Change Resiliency Planning For Water, Wastewater, and Stormwater, 2018 Successful Coproduction and Collaboration, 2018

Sea Level Rise Adaptation As the atmosphere warms due to climate change, there is a direct impact on the hydrologic cycle, thus creating unique challenges for the water sector. The effects of sea level rise and other associated coastal changes (e.g., storm surge, erosion, and flooding) have already had a wide range of impacts on coastal communities, and climate change will only exacerbate these challenges in the future. The hardships brought on by climate change are forcing a paradigm shift for decision-making in the water sector as practitioners seek to implement options to avoid, minimize, mitigate, and/or recover from the effects of these climate-driven impacts—an effort collectively known as adaptation. This guide is intended to provide tangible, replicable practices to help water utility staff and water resource managers advance adaptation efforts in the face of climate change. Sea level rise adaptation is context-specific (e.g., by location, by asset, and by system), and while there is no one-size-fits-all approach to adaptation, there are principles—or leading practices—that may help water sector practitioners move towards on-the-ground implementation. In this guide, implementation is defined as the process of making something active or effective that advances adaptation to sea level rise in a concrete way. This implies progress beyond understanding and assessing risk to executing policies (e.g., updated design standards), projects (e.g., building a desalination plant), process changes, or programs that proactively take action to boost resilience to climate impacts in the coastal zone (e.g., capacity building). Read the Report How to Use This Guide Water utilities and wholesale water providers do not function in a silo, and adaptation processes—from engagement to monitoring and evaluation of implemented strategies—must be coordinated with other municipal sectors and landowners, local organizations, tribal nations, community members, regional planning bodies, regulators, and all levels of government. Acknowledging this necessary coordination, this guide was developed with input from stakeholders in multiple sectors. Likewise, many of the leading practices and tools may be applicable beyond the water sector. However, leading practices particularly relevant to this field were chosen for inclusion, and it was developed from the water sector perspective with that audience in mind. It is meant to help other water utilities and resource managers begin implementing actions to adapt to sea level rise. This guide does: Provide a high-level overview of the general steps required to initiate sea level rise adaptation and includes resources and tools to support each step Detail the most frequent challenges encountered when reaching the point of implementation Suggest solutions based on leading practices for overcoming barriers, using real-life examples when possible This guide does not: Provide a detailed roadmap with all the necessary steps to achieve sea level rise adaptation Provide a deep dive into the technical aspects of sea level rise, such as the science behind projections, working with tide level data, or risk assessment methods Examine every aspect of how sea level rise and related issues may potentially affect your water utility or your geographic location Provide a step-by-step adaptation plan and strategy for specific utility assets or system types Overarching Themes Think big and outside the box . As our climate continues to change, we, as water utilities, must continue pushing the boundaries and strive for innovation. The status quo is not adequate. To truly address the magnitude of the climate crisis, we need to think creatively, beyond traditional solutions. Collaborate across siloes with a diverse set of stakeholders. Many of the leading practices highlighted here cannot be implemented by the water sector alone. Strong partnerships with other government agencies, stakeholders, and community members provide a space to include new voices to develop creative, effective, large-scale adaptation projects that address multiple issues and leverage resources. Incorporate flexibility and iteration in your adaptation planning and implementation. Adaptation planning to implementation is not a one-and-done process. With ever-changing information and considerable uncertainty, adaptation strategies must remain flexible and be re-evaluated often. The case studies highlighted in this guide often demonstrate where flexibility in the planning process can pay off in the long run by avoiding overinvestments. The ability to pivot as new information and resources become available can serve utilities well throughout the adaptation process. Consider all planning and decisions through an equity and environmental justice lens. Flooding hazards and the underlying causes of their disproportionate impact on vulnerable populations pose one of the biggest environmental justice challenges of our time. The climate crisis continues to exacerbate social inequities across our cities and communities, making them inextricably linked. Equitable, co-produced adaptation solutions are vital to ensuring our actions protect—and do not inadvertently harm—the communities we serve. Many of the leading practices in this guide touch upon equity and community engagement, yet it falls short of comprehensively viewing solutions through an equity lens. Going forward, we must shift our thinking to consider water and climate equity in everything we do.

Privacy Policy A legal disclaimer The explanations and information provided on this page are only general and high-level explanations and information on how to write your own document of a Privacy Policy. You should not rely on this article as legal advice or as recommendations regarding what you should actually do, because we cannot know in advance what are the specific privacy policies you wish to establish between your business and your customers and visitors. We recommend that you seek legal advice to help you understand and to assist you in the creation of your own Privacy Policy. Privacy Policy - the basics Having said that, a privacy policy is a statement that discloses some or all of the ways a website collects, uses, discloses, processes, and manages the data of its visitors and customers. It usually also includes a statement regarding the website’s commitment to protecting its visitors’ or customers’ privacy, and an explanation about the different mechanisms the website is implementing in order to protect privacy. Different jurisdictions have different legal obligations of what must be included in a Privacy Policy. You are responsible to make sure you are following the relevant legislation to your activities and location. What to include in the Privacy Policy Generally speaking, a Privacy Policy often addresses these types of issues: the types of information the website is collecting and the manner in which it collects the data; an explanation about why is the website collecting these types of information; what are the website’s practices on sharing the information with third parties; ways in which your visitors and customers can exercise their rights according to the relevant privacy legislation; the specific practices regarding minors’ data collection; and much, much more. To learn more about this, check out our article “Creating a Privacy Policy ”.

Equitable Climate Solutions Case Studies More intense storms, rising sea levels, and more frequent droughts can strain water supplies, damage infrastructure, threaten public health, and challenge the delivery of clean water, sanitation, and stormwater management. While climate and water resource challenges affect many communities, those already overburdened with economic, environmental, and health challenges are especially vulnerable. Those most affected often include Black, Indigenous, and Communities of Color, lower-income people, children, and the elderly, among others. Imbuing the climate action work of water utilities with an ethos of water equity can accelerate progress toward a resilient future for all. According to the US Water Alliance, water equity occurs when all communities have access to safe, clean, and affordable drinking water and wastewater services; are resilient in the face of floods, drought, and other climate risks; have a role in decision-making processes for water management in their communities; and share in the economic, social, and environmental benefits of water systems. The water sector is at the forefront of the climate crisis, and water, wastewater, and stormwater utilities have a critical role as anchor community institutions to center equity and climate resilience in all aspects of their water management. In recognition of the responsibility to help their communities thrive, utilities should recognize the links between water challenges, opportunities to advance equity, and the need for urgent yet thoughtful adaptation, resilience, and mitigation investments. To advance the work of the water sector on this topic and in support of WUCA's Strategic Plan, WUCA partnered with the US Water Alliance to develop a series of case studies that highlight leading practices for equitable climate action within the water sector and provide examples of how utilities are working with communities to address climate impacts and climate planning in equitable ways. The topics for each case study were co-developed by the WUCA Equity Committee and the US Water Alliance based on existing work and topics of interest from WUCA members. The selected topics span a wide range of key actions to achieve equity in climate resilience—some practices that are relatively well-known and understood, and others that are new avenues for action.Each case study provides key background information, select utility profiles, and a list of additional resources to support implementation. Utility profiles include detailed narratives of how leading utilities center equity in their climate adaptation efforts. The narratives were co-developed with each utility and feature key insights identified by the utility. Contact information is provided for each narrative to facilitate follow-up and enable interested readers to learn more about implementing similar projects. Leveraging Data for Equitable Climate Outcomes Community-informed data is an essential tool to promote accountability, social resilience, and equitable climate action in the water sector. Profiles of utility best practices include insights from Portland Water Bureau and Philadelphia Water Department. Equitable Community Engagement for Climate Action Equitable community engagement in the pursuit of empowered and authentic utility-community relationships underpins all equitable climate action work. Profiles of utility best practices include insights from Raleigh Stormwater, Seattle Public Utilities, and Austin Water Equity and Affordability in Water Conservation Affordability-focused household water conservation programs have the potential to promote community-wide water accessibility while supporting utility fiscal health and the long-term durability of water sources. Profiles of utility best practices include insights from Houston Public Works, Metropolitan Water District of Southern California, and San Diego County Water Authority. Climate Risk Disclosure for Equitable Climate Action Climate related challenges, including extreme weather, flooding, droughts, wildfires, and heatwaves, can undermine utilities' financial health, operational stability, and capacity to serve all in their communities equitably. These challenges necessitate efforts to assess, manage, and effectively communicate climate risks. Climate Investments that Support Underserved Communities Case studies highlight utilities that implement data-driven, community-informed strategies to bridge historical investment gaps and support those most vulnerable to the impacts of climate change.

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Engage Well-thought-out communication and engagement plans result in more effective, successful, and supported adaptation. Climate adaptation often requires field building and change management. As such, engaging internal and external stakeholders (two-way communication, listening and sharing) to motivate action, connect with and support others, and develop climate messages can go a long way toward making your adaptation efforts successful. The following leading practices are in the action area of ENGAGE and are described below: Recognize many ways to motivate climate adaptation action Seek out and support climate champions throughout your utility (also in SUSTAIN ) Consult expertise throughout your utility regularly and with purpose Tailor the climate adaptation message for the intended audience Develop a climate communications plan Include equity from the beginning Make the business case for climate adaptation (also in SUSTAIN ) ENGAGE Recognize many ways to motivate climate adaptation action Many things can motivate investment in climate adaptation, including climate champions, natural disasters or crises, peer and public pressure, personnel changes, personal observations of change, and access to new knowledge. Leverage the motivational opportunities that fit your circumstances. Example: Simultaneous natural disasters in Colorado In 2002, Denver Water saw unprecedented simultaneous natural disasters in its watersheds. During the single worst one-year drought ever recorded in Colorado, the largest wildfire the state had ever seen occurred in one of its largest and hardest working watersheds. Just weeks after the fire was contained, a rainstorm brought sedimentation and debris into streams and reservoirs, significantly impacting water quality and reservoir capacity. Now, nearly two decades later, the watershed is still noticeably scarred, and the memory of the 2002 natural disasters is still very present. While climate change did not cause these disasters, science tells us that recent warming contributed to their impacts. Overall, the experience helped Denver Water understand the importance of addressing climate change challenges. Now, dedicated staff actively work to understand and prepare for changes that may dramatically impact Denver Water's system and business model, such as continued warming and extreme heat; intensified droughts, floods, and forest fires; and changes to snowpack, Denver Water's high-elevation supply source. Example: Droughts and floods in Texas Austin, Texas, is prone to frequent droughts often followed by intense rainy periods. The most recent drought (2008-2016) dropped water levels in area reservoirs to near-record lows and ultimately surpassed the severity of the 1950s' drought of record. In some areas, lake levels were so low that it became difficult to launch boats and enjoy other water-based activities. The drought and high temperatures also took a visible toll on landscapes and other vegetation. Then, in 2018, historic flooding brought massive amounts of silt and dirt—over 100 times the typical level—into Austin's drinking water supply. This impacted raw water quality and slowed treatment systems. To ensure adequate flows in case of fires, Austin Water issued the first system-wide boil water notice in its 100-year history. With climate change, the utility expects these types of events to become more frequent and severe. Austin's leadership has long acknowledged and addressed climate impacts in its water planning efforts. The public has benefited, especially in the context of recent events, building momentum for additional actions. Most recently, the Austin City Council adopted Water Forward, an integrated water resource plan, which used a regional water supply context to develop strategies to ensure a sustainable and resilient water future into the next century. This experience can also help the abstract concept of climate change become more concrete. Example: Collective action because of a summit In January 2007, the San Francisco Public Utilities Commission (SF PUC) hosted the first national Water Utility Climate Change Summit, which was attended by more than 200 water and wastewater utility executives, government officials, climate change experts and environmental leaders. The purpose of the gathering was to help participants better understand the impacts of climate change on water-related infrastructure and water resource supplies. During that summit, utility leaders recognized the future risks and value a collective effort would bring to the climate adaptation conversation. As the summit drew to a close, SF PUC General Manager Susan Leal committed to fund an effort from the dais and issued a challenge to attendees. Turning to Metropolitan Water District of Southern California General Manager Jeff Kightlinger, who had served on a panel but was now back in his seat among the audience of 200, she said: "Jeff?" Kightlinger replied, "Sounds good to me!" and turned to his Board Chair, Tim Brick, who was also in the audience, and said "Tim?" Brick gave his thumbs up, Metropolitan matched the San Francisco Public Utilities Commission's pledge, and planning for what became WUCA began. (Interesting note: that initial pledge lasted nearly ten years because the bulk of WUCA's work has been driven by utility staff and volunteer experts drawn into the collaboration). Shortly after the summit, WUCA was formed, which has led to over a decade of innovative work in climate adaptation, as highlighted throughout these leading practices. ENGAGE SUSTAIN Seek out and support climate champions throughout your utility Progress happens more quickly with the support of motivated individuals who value and prioritize climate adaptation work, including executive-level leaders. It is therefore important to build relationships with and educate champions who can influence climate adaptation actions, then help sustain and strengthen those efforts. Having champions across an organization (in planning, engineering, finance, public relations, and other roles) can contribute diverse expertise and resources and help provide institutional memory as individuals' roles change. This practice is included under both ENGAGE and SUSTAIN climate adaptation actions. Example: Building a cross-functional team of champions The Central Arizona Project (CAP) climate adaptation plan(Opens another site in new window) was developed with an education and engagement mindset, which elevated existing and promoted future climate champions throughout the organization. Key to the development of the plan was the active participation of a cross-functional team of internal experts comprising all of CAP's climate-sensitive functions, including water policy, operations and engineering, maintenance, public affairs, technology, legal services, finance and administration, and employee services. The team collaboratively identified implications of climate change for CAP's functions as well as all components of the CAP climate adaptation plan. This approach helped foster climate champions in each of CAP's organizational functions by actively educating and engaging them in the climate adaptation process. It also gave members of the CAP team ownership in addressing CAP's climate challenges. Example: Interactive climate education with an organization One important way to build climate champions is through interactive climate education sessions within an organization. For example, Denver Water includes a "Climate 101" unit in all orientation sessions for new employees and provides climate science, adaptation, and mitigation information in its new employee onboarding package. As part of the Climate 101 education sessions, new employees are given prompts to brainstorm how climate change could impact various utility business functions (finance, water treatment, construction, etc.). This approach gets employees thinking creatively about climate change from day one of the job and establishes a baseline level of climate knowledge. After a Climate 101 session, a new employee of Denver Water's youth education team was inspired to integrate climate change into the youth education curriculum and has since created an entire climate change and water module that is presented to schools throughout the region. Building on the successful implementation of these Climate 101 sessions for new employees, the climate team began offering the sessions to other sections at the utility, usually in groups of three to five people to allow for more interactive conversation. This small scale and interactive approach to climate education has allowed the climate team to build climate champions throughout the organization, as well as to build relationships and co-produce climate adaptation ideas with subject matter experts from many business functions. Example: A dedicated person to support champions utility-wide Austin Water has a long history of implementing a variety of climate planning and management measures. While these efforts have traditionally been housed in the Environmental Affairs and Conservation Program Area, climate work has also been done across utility program areas—like Operations, Pipeline Engineering, and Water Resources Management—and, to some extent, in different city departments. In 2019, Austin Water established a new staff position, Climate Protection Consultant, to place additional utility-wide focus on climate issues. This includes taking steps to enhance information sharing about climate change across the utility, continuing to better incorporate climate concerns into cross-functional utility planning efforts, and representing Austin Water on city-wide climate planning initiatives. This position reports to the Assistant Director of Environmental, Planning, and Development Services. This reporting structure provides frequent opportunities for sharing climate-related information with utility leadership. In addition, the Office of Sustainability, a department within the City of Austin, is currently evaluating options for creating a new Chief Climate Resilience Officer position to address city-wide climate resilience planning and strategy implementation. ENGAGE Consult expertise throughout your utility regularly and with purpose Adapting to climate change requires diverse expertise and broad participation, both of which can be gained by consulting others throughout your organization. The type of engagement that works best varies depending on an organization's culture, but a little forethought and some regularity can go a long way (e.g., begin with listening and ask what matters). Example: Business function conversations Southern Nevada Water Authority (SNWA) climate adaptation staff initiated a process of engagement with internal experts by first sharing results from a region-specific climate change projection study. At early meetings, department heads learned about the types of changes expected in the future and weighed in on how these changes might impact utility business functions. From these initial meetings, a few key business function areas were identified to develop adaptation actions. Then, SNWA set up small group meetings and interviewed each business function area to gather how the organization's experts thought they could address potential impacts. Conversations were summarized, and each small group reviewed the recommended actions and helped develop next steps. The process accomplished several goals: It educated staff about climate change It introduced staff to SNWA's climate leadership so they know whom to contact in the organization with questions Because business function experts were the ones to develop the solutions, it ensures buy-in and increases the likelihood that proposed solutions will be implemented See Example: Business function mapping to learn about a framework for considering climate change across an organization’s business functions. Example: Trash removal as an unexpected adaptation need Adaptation planners at the Philadelphia Water Department (PWD) recognized that successful adaptation requires expertise on both climate science and operations. It is not possible for PWD's adaptation planners to possess all of the necessary operational knowledge for the numerous systems PWD operates and maintains across the city (drinking water, wastewater, and stormwater). So the PWD Climate Change Adaptation Program (CCAP) prioritized engaging in two-way conversations with utility operators early and often to share information and begin developing meaningful solutions/adaptation strategies. For example, PWD's adaptation planners met with operations staff at one of PWD's wastewater treatment plants. After presenting future projections of precipitation increases, the operators shared that these conditions would likely produce more trash, accumulating at faster rates, during the initial screening stage of the wastewater treatment process. This consequence, which was only identified after consulting with plant operators, has implications for resources—more staff and equipment may be needed to remove and process trash to maintain current levels of service. Example: Utility-wide climate adaptation planning Preparing a Climate Adaptation Plan provides an opportunity to form a cross-functional team with a clear purpose (see ENGAGE: Seek out and support climate champions throughout your utility). Important lessons Have well-organized information for people to react to. However, do not wait for the analysis to be perfect—share what you have along the way. Strike the right balance between reaching out to staff and respecting their time. ENGAGE Tailor the climate adaptation message for the intended audience One key to successful communication is knowing your audience(s) and framing your message so it has meaning and value to them. A climate adaptation message that resonates with one individual or group might not "land" with others. Identifying which messages work best is time well spent. Example: Be clear why climate change matter Over the past 10 years, the Alliance has homed in on messages that resonate with water utilities to demonstrate the impact climate change could have on critical utility operations and functions. Powerful, clear messages that connect climate change to water utility responsibilities include climate change is water change and warming is here and now. Example: Messages that resonate with engineers When the Philadelphia Water Department (PWD) Climate Change Adaptation Program (CCAP) was ready to share information and results from analyses internally, success—i.e., whether climate information would eventually be adopted within existing planning, design, and asset management processes—hinged on good communication. For example, when sharing information with engineers who work on long-term infrastructure plans, CCAP first explained how climate change is altering the water cycle and how climate non-stationarity might challenge standard engineering practices, procedures, and tools. Planners and design engineers are used to working with return intervals and other statistical tools and methods that are based on historic data. It was essential to explain that, because of climate change, these traditional tools and methods may no longer be adequate moving forward. It was also important to convey that the CCAP team is available to help PWD staff tackle these challenges. Example: Concrete impacts of warming temperatures Climate change can be an abstract concept for water utility professionals whose daily responsibilities include operating reservoirs, designing and building projects, and managing aging infrastructure. To make climate change concrete, the Portland Water Bureau has identified a spectrum of ways in which climate warming and its impacts affect water utility functions and operations, from engineering and operations groups to finance, communications, and maintenance & construction. For example, climate warming and wildfire smoke directly affect the health and safety of the outdoor workforce. Also, increased risk of flooding and landslides could damage critical bureau assets. Presenting direct impacts to the day-to-day job of construction field crews and asset management engineers has successfully resonated with these staff. To recognize these impacts and the need for adaptation more formally, the Portland Water Bureau has included several climate adaptation strategies in the utility’s updated strategic plan. The utility also gives many internal and external presentations within the water sector, and most of these communications begin by connecting the physics of a warmer atmosphere to the hydrologic cycle. From there it is easier to illustrate how a changing water cycle will affect a given water utility. ENGAGE Develop a climate communications plan Taking time to consider how climate change information and adaptations strategies are communicated both internally and externally can help motivate action and avoid conflict or confusion. ENGAGE Include equity from the beginning Effective solutions to climate change challenges depend on many factors, all of which might not be clear at the onset. Engaging and focusing on the needs of communities, particularly those most vulnerable to disruptions caused by climate impacts, is best done at the beginning and throughout a project. By improving conditions for the most vulnerable in your community, you also improve conditions for everyone. ENGAGE SUSTAIN Make the business case for climate adaptation Improving resiliency takes time and resources but can also save time and resources. Transparency about financial elements, including tradeoffs in costs and other triple-bottom-line benefits — social, environmental, and financial — can motivate action and demonstrate how adaptation investments can save money in the long run. This helps engage people from the beginning and sustain the effort. This practice is included under both ENGAGE and SUSTAIN climate adaptation actions. See examples in the SUSTAIN section.

Engage Well-thought-out communication and engagement plans result in more effective, successful, and supported adaptation. Climate adaptation often requires field building and change management. As such, engaging internal and external stakeholders (two-way communication, listening and sharing) to motivate action, connect with and support others, and develop climate messages can go a long way toward making your adaptation efforts successful. The following leading practices are in the action area of ENGAGE and are described below: Recognize many ways to motivate climate adaptation action Seek out and support climate champions throughout your utility (also in SUSTAIN ) Consult expertise throughout your utility regularly and with purpose Tailor the climate adaptation message for the intended audience Develop a climate communications plan Include equity from the beginning Make the business case for climate adaptation (also in SUSTAIN ) ENGAGE Recognize many ways to motivate climate adaptation action Many things can motivate investment in climate adaptation, including climate champions, natural disasters or crises, peer and public pressure, personnel changes, personal observations of change, and access to new knowledge. Leverage the motivational opportunities that fit your circumstances. Example: Simultaneous natural disasters in Colorado In 2002, Denver Water saw unprecedented simultaneous natural disasters in its watersheds. During the single worst one-year drought ever recorded in Colorado, the largest wildfire the state had ever seen occurred in one of its largest and hardest working watersheds. Just weeks after the fire was contained, a rainstorm brought sedimentation and debris into streams and reservoirs, significantly impacting water quality and reservoir capacity. Now, nearly two decades later, the watershed is still noticeably scarred, and the memory of the 2002 natural disasters is still very present. While climate change did not cause these disasters, science tells us that recent warming contributed to their impacts. Overall, the experience helped Denver Water understand the importance of addressing climate change challenges. Now, dedicated staff actively work to understand and prepare for changes that may dramatically impact Denver Water's system and business model, such as continued warming and extreme heat; intensified droughts, floods, and forest fires; and changes to snowpack, Denver Water's high-elevation supply source. Example: Droughts and floods in Texas Austin, Texas, is prone to frequent droughts often followed by intense rainy periods. The most recent drought (2008-2016) dropped water levels in area reservoirs to near-record lows and ultimately surpassed the severity of the 1950s' drought of record. In some areas, lake levels were so low that it became difficult to launch boats and enjoy other water-based activities. The drought and high temperatures also took a visible toll on landscapes and other vegetation. Then, in 2018, historic flooding brought massive amounts of silt and dirt—over 100 times the typical level—into Austin's drinking water supply. This impacted raw water quality and slowed treatment systems. To ensure adequate flows in case of fires, Austin Water issued the first system-wide boil water notice in its 100-year history. With climate change, the utility expects these types of events to become more frequent and severe. Austin's leadership has long acknowledged and addressed climate impacts in its water planning efforts. The public has benefited, especially in the context of recent events, building momentum for additional actions. Most recently, the Austin City Council adopted Water Forward, an integrated water resource plan, which used a regional water supply context to develop strategies to ensure a sustainable and resilient water future into the next century. This experience can also help the abstract concept of climate change become more concrete. Example: Collective action because of a summit In January 2007, the San Francisco Public Utilities Commission (SF PUC) hosted the first national Water Utility Climate Change Summit, which was attended by more than 200 water and wastewater utility executives, government officials, climate change experts and environmental leaders. The purpose of the gathering was to help participants better understand the impacts of climate change on water-related infrastructure and water resource supplies. During that summit, utility leaders recognized the future risks and value a collective effort would bring to the climate adaptation conversation. As the summit drew to a close, SF PUC General Manager Susan Leal committed to fund an effort from the dais and issued a challenge to attendees. Turning to Metropolitan Water District of Southern California General Manager Jeff Kightlinger, who had served on a panel but was now back in his seat among the audience of 200, she said: "Jeff?" Kightlinger replied, "Sounds good to me!" and turned to his Board Chair, Tim Brick, who was also in the audience, and said "Tim?" Brick gave his thumbs up, Metropolitan matched the San Francisco Public Utilities Commission's pledge, and planning for what became WUCA began. (Interesting note: that initial pledge lasted nearly ten years because the bulk of WUCA's work has been driven by utility staff and volunteer experts drawn into the collaboration). Shortly after the summit, WUCA was formed, which has led to over a decade of innovative work in climate adaptation, as highlighted throughout these leading practices. ENGAGE SUSTAIN Seek out and support climate champions throughout your utility Progress happens more quickly with the support of motivated individuals who value and prioritize climate adaptation work, including executive-level leaders. It is therefore important to build relationships with and educate champions who can influence climate adaptation actions, then help sustain and strengthen those efforts. Having champions across an organization (in planning, engineering, finance, public relations, and other roles) can contribute diverse expertise and resources and help provide institutional memory as individuals' roles change. This practice is included under both ENGAGE and SUSTAIN climate adaptation actions. Example: Building a cross-functional team of champions The Central Arizona Project (CAP) climate adaptation plan(Opens another site in new window) was developed with an education and engagement mindset, which elevated existing and promoted future climate champions throughout the organization. Key to the development of the plan was the active participation of a cross-functional team of internal experts comprising all of CAP's climate-sensitive functions, including water policy, operations and engineering, maintenance, public affairs, technology, legal services, finance and administration, and employee services. The team collaboratively identified implications of climate change for CAP's functions as well as all components of the CAP climate adaptation plan. This approach helped foster climate champions in each of CAP's organizational functions by actively educating and engaging them in the climate adaptation process. It also gave members of the CAP team ownership in addressing CAP's climate challenges. Example: Interactive climate education with an organization One important way to build climate champions is through interactive climate education sessions within an organization. For example, Denver Water includes a "Climate 101" unit in all orientation sessions for new employees and provides climate science, adaptation, and mitigation information in its new employee onboarding package. As part of the Climate 101 education sessions, new employees are given prompts to brainstorm how climate change could impact various utility business functions (finance, water treatment, construction, etc.). This approach gets employees thinking creatively about climate change from day one of the job and establishes a baseline level of climate knowledge. After a Climate 101 session, a new employee of Denver Water's youth education team was inspired to integrate climate change into the youth education curriculum and has since created an entire climate change and water module that is presented to schools throughout the region. Building on the successful implementation of these Climate 101 sessions for new employees, the climate team began offering the sessions to other sections at the utility, usually in groups of three to five people to allow for more interactive conversation. This small scale and interactive approach to climate education has allowed the climate team to build climate champions throughout the organization, as well as to build relationships and co-produce climate adaptation ideas with subject matter experts from many business functions. Example: A dedicated person to support champions utility-wide Austin Water has a long history of implementing a variety of climate planning and management measures. While these efforts have traditionally been housed in the Environmental Affairs and Conservation Program Area, climate work has also been done across utility program areas—like Operations, Pipeline Engineering, and Water Resources Management—and, to some extent, in different city departments. In 2019, Austin Water established a new staff position, Climate Protection Consultant, to place additional utility-wide focus on climate issues. This includes taking steps to enhance information sharing about climate change across the utility, continuing to better incorporate climate concerns into cross-functional utility planning efforts, and representing Austin Water on city-wide climate planning initiatives. This position reports to the Assistant Director of Environmental, Planning, and Development Services. This reporting structure provides frequent opportunities for sharing climate-related information with utility leadership. In addition, the Office of Sustainability, a department within the City of Austin, is currently evaluating options for creating a new Chief Climate Resilience Officer position to address city-wide climate resilience planning and strategy implementation. ENGAGE Consult expertise throughout your utility regularly and with purpose Adapting to climate change requires diverse expertise and broad participation, both of which can be gained by consulting others throughout your organization. The type of engagement that works best varies depending on an organization's culture, but a little forethought and some regularity can go a long way (e.g., begin with listening and ask what matters). Example: Business function conversations Southern Nevada Water Authority (SNWA) climate adaptation staff initiated a process of engagement with internal experts by first sharing results from a region-specific climate change projection study. At early meetings, department heads learned about the types of changes expected in the future and weighed in on how these changes might impact utility business functions. From these initial meetings, a few key business function areas were identified to develop adaptation actions. Then, SNWA set up small group meetings and interviewed each business function area to gather how the organization's experts thought they could address potential impacts. Conversations were summarized, and each small group reviewed the recommended actions and helped develop next steps. The process accomplished several goals: It educated staff about climate change It introduced staff to SNWA's climate leadership so they know whom to contact in the organization with questions Because business function experts were the ones to develop the solutions, it ensures buy-in and increases the likelihood that proposed solutions will be implemented See Example: Business function mapping to learn about a framework for considering climate change across an organization’s business functions. Example: Trash removal as an unexpected adaptation need Adaptation planners at the Philadelphia Water Department (PWD) recognized that successful adaptation requires expertise on both climate science and operations. It is not possible for PWD's adaptation planners to possess all of the necessary operational knowledge for the numerous systems PWD operates and maintains across the city (drinking water, wastewater, and stormwater). So the PWD Climate Change Adaptation Program (CCAP) prioritized engaging in two-way conversations with utility operators early and often to share information and begin developing meaningful solutions/adaptation strategies. For example, PWD's adaptation planners met with operations staff at one of PWD's wastewater treatment plants. After presenting future projections of precipitation increases, the operators shared that these conditions would likely produce more trash, accumulating at faster rates, during the initial screening stage of the wastewater treatment process. This consequence, which was only identified after consulting with plant operators, has implications for resources—more staff and equipment may be needed to remove and process trash to maintain current levels of service. Example: Utility-wide climate adaptation planning Preparing a Climate Adaptation Plan provides an opportunity to form a cross-functional team with a clear purpose (see ENGAGE: Seek out and support climate champions throughout your utility). Important lessons Have well-organized information for people to react to. However, do not wait for the analysis to be perfect—share what you have along the way. Strike the right balance between reaching out to staff and respecting their time. ENGAGE Tailor the climate adaptation message for the intended audience One key to successful communication is knowing your audience(s) and framing your message so it has meaning and value to them. A climate adaptation message that resonates with one individual or group might not "land" with others. Identifying which messages work best is time well spent. Example: Be clear why climate change matter Over the past 10 years, the Alliance has homed in on messages that resonate with water utilities to demonstrate the impact climate change could have on critical utility operations and functions. Powerful, clear messages that connect climate change to water utility responsibilities include climate change is water change and warming is here and now. Example: Messages that resonate with engineers When the Philadelphia Water Department (PWD) Climate Change Adaptation Program (CCAP) was ready to share information and results from analyses internally, success—i.e., whether climate information would eventually be adopted within existing planning, design, and asset management processes—hinged on good communication. For example, when sharing information with engineers who work on long-term infrastructure plans, CCAP first explained how climate change is altering the water cycle and how climate non-stationarity might challenge standard engineering practices, procedures, and tools. Planners and design engineers are used to working with return intervals and other statistical tools and methods that are based on historic data. It was essential to explain that, because of climate change, these traditional tools and methods may no longer be adequate moving forward. It was also important to convey that the CCAP team is available to help PWD staff tackle these challenges. Example: Concrete impacts of warming temperatures Climate change can be an abstract concept for water utility professionals whose daily responsibilities include operating reservoirs, designing and building projects, and managing aging infrastructure. To make climate change concrete, the Portland Water Bureau has identified a spectrum of ways in which climate warming and its impacts affect water utility functions and operations, from engineering and operations groups to finance, communications, and maintenance & construction. For example, climate warming and wildfire smoke directly affect the health and safety of the outdoor workforce. Also, increased risk of flooding and landslides could damage critical bureau assets. Presenting direct impacts to the day-to-day job of construction field crews and asset management engineers has successfully resonated with these staff. To recognize these impacts and the need for adaptation more formally, the Portland Water Bureau has included several climate adaptation strategies in the utility’s updated strategic plan. The utility also gives many internal and external presentations within the water sector, and most of these communications begin by connecting the physics of a warmer atmosphere to the hydrologic cycle. From there it is easier to illustrate how a changing water cycle will affect a given water utility. ENGAGE Develop a climate communications plan Taking time to consider how climate change information and adaptations strategies are communicated both internally and externally can help motivate action and avoid conflict or confusion. ENGAGE Include equity from the beginning Effective solutions to climate change challenges depend on many factors, all of which might not be clear at the onset. Engaging and focusing on the needs of communities, particularly those most vulnerable to disruptions caused by climate impacts, is best done at the beginning and throughout a project. By improving conditions for the most vulnerable in your community, you also improve conditions for everyone. ENGAGE SUSTAIN Make the business case for climate adaptation Improving resiliency takes time and resources but can also save time and resources. Transparency about financial elements, including tradeoffs in costs and other triple-bottom-line benefits — social, environmental, and financial — can motivate action and demonstrate how adaptation investments can save money in the long run. This helps engage people from the beginning and sustain the effort. This practice is included under both ENGAGE and SUSTAIN climate adaptation actions. See examples in the SUSTAIN section.

CMIP6 Frequently Asked Questions: A Resource for Water Managers CMIP6 (Coupled Model Intercomparison Project, Phase 6) is the most recent organized international "roundup" of global climate projections from several dozen climate models. The models are run using standardized input scenarios (e.g., of greenhouse gas emissions and other climate drivers) to produce thousands of simulations of past and future climate conditions that get widely used in climate research, assessment, and adaptation planning. The WUCA CMIP6 Working Group sought out specialists to develop a CMIP6 Frequently Asked Questions (FAQ) document for water managers which would assume little or no previous experience with CMIP6 and other climate-model datasets. The goal was to develop a dozen or so highly relevant questions — and clear responses — to aid in the use and interpretation of CMIP6 datasets, with a focus on the contiguous United States. The FAQs were initially proposed by Working Group members, and then iteratively refined in collaboration with the Working Group, resulting in 13 questions. The document benefited considerably from reviews by the CMIP6 Working Group and by external subject matter experts. Each question has a "short answer" (1–2 paragraphs) and a "long answer" (2–5 pages), including figures where appropriate, recommendations for further reading, and other references. Read the FAQ Excerpt from the FAQ: What studies have already been conducted using CMIP6 byor on behalf of water agencies? What was learned about CMIP6? Short answer As of Fall 2024, a handful of research and assessment efforts using CMIP6 have been conducted by or on behalf of water agencies in Oregon, Colorado, and Florida. More studies will be coming out soon. Long answer Below are short overviews of the studies and assessments to date and their key findings. CMIP6 model performance over the Pacific Northwest (Taylor et al. 2023; Portland Water Bureau). Supported in part by Portland Water Bureau, Taylor et al. (2023) analyzed the raw output of 25 CMIP6 models to evaluate their fidelity in simulating several common, large-scale atmospheric circulation patterns (e.g., low- and high-pressure systems) that drive seasonal precipitation anomalies in the Pacific Northwest. They found that the CMIP6 models are generally able to simulate the range of observed circulation patterns with reasonable fidelity, although model skill varies across the ensemble. This generates confidence that the models, when simulating regional precipitation and temperature anomalies, do so for the correct physical reasons. They did not, however, compare the CMIP6 models’ performance with CMIP5 models. Climate Change in Colorado (Bolinger et al. 2024; Colorado Water Conservation Board) The 3rd edition of the Climate Change in Colorado report (Bolinger et al. 2024), produced in partnership with the Colorado Water Conservation Board, compared raw CMIP5 (36 models) and CMIP6 (37 models) projections of statewide-average change in annual temperature andannual precipitation, under 4.5 emissions scenarios. Figure 13.1. Projected change in Colorado statewide average annual temperatures to 2100,relative to a 1971–2000 baseline, from raw CMIP5 model output (median and range) andraw, unscreened CMIP6 model output (median only) under medium-low emissionsscenarios (RCP4.5, SSP2-4.5), compared to observed temperatures through 2022. Themedian warming seen in CMIP6 diverges from the CMIP5 median after 2020, with thedifference increasing to ~1.0°F by 2070. (Figure 2.7 in Bolinger et al. 2024) The results of this Colorado-focused comparison were consistent with results of the CONUS-wide and regional comparisons described in Q7: The CMIP6 ensemble range was overall shifted warmer (Figure 13.1) and slightly wetter relative to CMIP5, with substantial overlap between the ensemble ranges. Screening out CMIP6 hot models (using Likely TCR) reduced the warming gap between CMIP6 and CMIP5 by ~50%, but had no effect on the CMIP6 precipitation change. After screening, CMIP6 was still slightly warmer and slightly wetter than CMIP5 for Colorado, so modeled hydrologic outcomes using screened CMIP6 CMIP6 vs CMIP5 model performance: Florida precipitation (Wang and Asefa 2024; Tampa Bay Water) Wang and Asefa (both with Tampa Bay Water) assessed the performance of 18 CMIP5 and 27 CMIP6 models in simulating historical monthly precipitation for 24 grid boxes across Florida.They found that the CMIP6 models, overall, were significantly better than the CMI5 models in terms of bias (too much/too little) in simulated monthly average precipitation, simulation of the seasonal cycle of precipitation, and simulation of the onset and end of the summer rainyseason. Spatially, in both CMIP6 and CMIP5, precipitation over the Peninsula was better simulated than precipitation over the Panhandle. Short Answers to FAQs 1. What is CMIP 6? CMIP6 (Coupled Model Intercomparison Project, Phase 6) is the most recent organized international "roundup" of global climate projections from several dozen climate models. The models are run using standardized input scenarios (e.g., of greenhouse gas emissions and other climate drivers) to produce thousands of simulations of past and future climate conditions that get widely used in climate research, assessment, and adaptation planning. 2. How is CMIP6 different from CMIP5, and is CMIP6 better? Short answer CMIP6 differs from CMIP5 in several ways, although these differences do not set CMIP6 completely apart from its predecessors. CMIP6 models generally have higher spatial resolution and greater complexity than their CMIP5 counterparts, although the range in those attributes across the CMIP6 ensemble overlaps with the CMIP5 range. For measures of model performance, general improvements are seen in CMIP6, again with substantial overlap between the CMIP6 and CMIP5 ensembles. CMIP6 does include projections under a greater diversity of emissions scenarios than CMIP5 (8 vs. 4) and includes many more model runs per model/scenario pairing, on average. As climate modeling continues to develop and mature, the overall improvement represented by a new CMIP has become smaller. CMIP6 is better overall than CMIP5 by many measures, but not by so much as to make CMIP5 obsolete. Depending on the specific use case, there may be compelling reasons to use data from CMIP6 or CMIP5, aside from the qualities of the models themselves. 3. What is the CMIP6 hot-model issue, and what are its implications for users? Short answer About one-quarter of the CMIP6 models show greater future warming, given comparable emissions scenarios, than even the hottest-running models in the CMIP5 or CMIP3 ensembles. Most of these "hot" CMIP6 models also simulate recent global warming (1980 to 2015) that is greater than the instrumentally observed global warming over that period. Follow-up studies and other evidence suggest that the very high rate of warming seen in the hot CMIP6 models may be physically implausible. Due to the inclusion of these hot models, CMIP6 shows substantially warmer projected futures, on average, in nearly all locations globally, including in the U.S., than CMIP5 under comparable emissions scenarios. Several methods have been developed to screen or weight the hot models, reducing their influence, as the IPCC authors did in the latest AR6 reports. However, it is not clear that the hot models' picture of an extremely warm future should be discounted. Also, screening or weighting the hot models may not be appropriate for regional analyses of precipitation and other non-temperature variables. Note that even with the hot models removed, the CMIP6 model ensemble is still somewhat warmer than CMIP5 (see question 7). 4. What are the emissions scenarios in CMIP6 and how do they differ from CMIP5 scenarios? Short answer The CMIP climate modeling approach uses multiple emissions scenarios as model inputs to represent deep uncertainty in the future socioeconomic and policy conditions that will drive the trajectory of greenhouse gas (GHG) emissions and concentrations in the atmosphere over the 21st century and beyond. Each emissions scenario encodes a different degree of anthropogenic influence on the climate (i.e., radiative forcing). Which emissions scenario we end up closest to — and thus the severity of the warming we experience — largely depends on how much additional GHG emissions our collective activities produce. In addition to GHGs, the scenarios specify future changes in land use and anthropogenic aerosols. For CMIP6, there were eight such scenarios under which the models were run, spanning a broad range of potential future trajectories. Four of the eight CMIP6 scenarios (SSP1-2.6, SSP2-4.5, SSP4-6.0, and SSP5-8.5) are roughly comparable to the four RCP scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5) used in CMIP5. 5. Which CMIP6 emissions scenarios (SSPs) should be used in an analysis? Short answer The decision of which SSP(s) to use in an analysis should consider several aspects of the scenarios and the intended application, including scenario likelihood, data availability, planning horizon, consistency with previous analyses, and risk tolerance and system vulnerability. Scenario likelihood — which scenarios are more likely to occur, given recent trends in emissions and current policies — is a key consideration for most planning applications. On that basis alone, SSP2-4.5 and SSP4-6.0 would be advisable, followed by SSP4-3.4, with SSP3-7.0 as a potential high-stress scenario. However, there is less output (fewer models/projections) available for SSP4-6.0 and SSP4-3.4 than for SSP2-4.5 and SSP3-7.0. Since the climate outcomes for each SSP increasingly diverge over time, for any analyses focused on later time horizons (~2060 onward) the choice of SSPs is more consequential than for analyses centered earlier in the 21st century. 6. What are Global Warming Levels (GWLs) and how do they correspond to the CMIP6 emissions scenarios? Short answer Global Warming Levels (GWLs) are a relatively new approach for analyzing and communicating regional-to-local climate changes that sidesteps the questions of exactly when those changes might happen and under what emissions scenarios. GWL-based analyses are typically displayed as maps or tables. They show the spatial pattern of projected future changes in a particular variable (e.g., extreme precipitation) that are associated with a particular increment of globally averaged warming, such as +2°C (+3.6°F). GWL-based analyses can provide a versatile framework for risk assessment but may require some adaptation to use in more traditional long-range planning centered on a specific time horizon. https://static.wixstatic.com/media/b5ae68_f360bd0ec6c24f60a6e8e17ffb97f002~mv2.png Figure 6.1. Example of a Global Warming Level (GWL) analysis: Projected future increase in the number of days per year over 35°C (95°F) at a GWL of 2°C, based on the mean projection from 27 CMIP6 models. (Source: Modified from IPCC WGI Interactive Atlas(https://interactive-atlas.ipcc.ch/) 7. Does CMIP6 show different future climate outcomes for the U.S. than CMIP5, given comparable emissions scenarios? Short answer For projected future temperature and precipitation for the U.S., the differences between the CMIP5 and CMIP6 ensemble means are relatively small compared to the overlap between the two ensembles of global models. The respective spatial patterns of projected temperature and precipitation change for CMIP5 and CMIP6 are also very similar. (Robust comparisons of fine-scale hydrologic changes between CMIP5 and CMIP6 are not feasible with existing datasets as of Fall 2024.) That said, in the preliminary comparisons, the CMIP6 ensemble mean and median show greater warming for the major U.S. regions than the mean and median for CMIP5. This also holds true for most locations in the U.S., even after screening or weighting models for the hot-model issue (Q3). The differences in projected temperature are large enough that CMIP6-based analyses may show appreciably greater temperature-related vulnerabilities — and potentially greater hydrology-related vulnerabilities as well — than the equivalent CMIP5-based analyses. 8. How does the level of uncertainty in CMIP6 compare with CMIP5? Short answer There are several sources of uncertainty in any set of future climate and hydrology projections at local-to-regional scales (e.g., emissions scenario uncertainty, model uncertainty, natural variability uncertainty). An especially important one to consider in comparing CMIP6 with CMIP5 is model uncertainty, sometimes called structural uncertainty. The model uncertainties in projected future temperature can be characterized by the spread of projected changes across the model ensemble. By this measure, model uncertainties seen in CMIP6 are of similar magnitude to CMIP5, given comparable emissions scenarios and comparably sized model ensembles. However, the total uncertainty in a CMIP6-based analysis of local climate and hydrology changes could differ from the uncertainty in a CMIP5- based analysis for multiple reasons beyond the climate models themselves. Also, consulting a larger number of models will typically reveal greater uncertainty. 9. Should CMIP6 or CMIP5 be used in a new analysis? Should existing CMIP5 analyses be updated with CMIP6? Short answer If a new analysis of climate projections is required, then it makes sense to use CMIP6, assuming the desired type and spatial scale of CMIP6-based data are accessible. Downscaled hydrologic model output based on CMIP6, for example, is not yet widely available. It is not usually necessary, however, to update existing CMIP5-based analyses just for the sake of using the latest CMIP projections. That said, updating an analysis to CMIP6 also provides an opportunity to implement enhancements in other data-processing and modeling steps. 10. What CMIP6 datasets are available for visualization and/or download, and where can they be accessed? Short answer The primary Earth System Grid Federation (ESGF) archive of original-resolution (raw) CMIP6 projections is available to any user, but the archive is enormous and challenging to navigate, and the data files are very large. Alternatively, the CMIP6 portals on Amazon Web Services and Google Cloud host the ESGF data files and allow users to perform analyses in the cloud, but these portals require high skill in data handling as well. More manageable partial archives of raw CMIP6 projections are available from three other portals where users can visualize the data prior to downloading, with options for spatial and temporal clipping and averaging of the data. A handful of higher-resolution, downscaled CMIP6 datasets are also available for global or U.S./North American domains. These are value-added products based on subsets of the primary raw CMIP6 archive and are produced by research groups outside of the CMIP framework. Only one downscaled dataset (LOCA2) is currently accessible through a visualization portal (USGS National Climate Change Viewer; the other datasets are download only). More options for downscaled data are likely to become available soon. https://static.wixstatic.com/media/b5ae68_92f35aec8209439fbc2673f3559feebf~mv2.png Figure 10.1. Schematic showing selected CMIP6 datasets that are currently available as of Fall 2024, as matched with user needs and characteristics. See “Long answer” below for more details and links to these datasets. 11. What additional CMIP6 downscaling and modeling efforts are in progress? What new capabilities will they provide? Short answer As of Fall 2024, there are several CMIP6 downscaling efforts in progress that once completed will provide new capabilities: variables that are not available from other datasets, expanded visualization and data-handling options, and/or more physically realistic simulation of finescale processes and changes. 12. How can under-resourced communities and water providers best use CMIP6 (and/or CMIP5)? Are there specific resources that enable easier access to, and interpretation of, local or regional climate projections? Short answer When resources are limited, it may be more effective to use those resources to better understand a community’s or water system’s vulnerabilities and impact thresholds, rather than to perform new localized analyses of CMIP projections. Relevant climate change information can often be obtained "off-the-shelf," in climate assessments and similar resources. These resources include interpretation of the projected climate changes alongside curated graphics and key findings and messages. 13. What studies have already been conducted using CMIP6 by or on behalf of water agencies? What was learned about CMIP6? Short answer As of Fall 2024, a handful of research and assessment efforts using CMIP6 have been conducted by or on behalf of water agencies in Oregon, Colorado, and Florida. More studies will be coming out soon.