California’s Water Systems: A Complex Network Facing Climate Challenges
Authored by: Rebecca Berg, Policy Associate and Krystle Golly, Sustainable Programs Senior Manager
California’s water systems have recently made national headlines as communities were devastated by wildfires fueled by unprecedented Santa Ana winds in January of this year. Climate change has increased the frequency and severity of wildfires in California1, while also causing more severe droughts and floods2. The State of California has developed adaptation and mitigation plans to try to prepare the state for these intense weather events, and properly respond to them when they do happen. When it comes to wildfire and water management, it may seem as though the obvious solution is to transport more water from the water-rich Northern California to the arid regions of Southern California, particularly Los Angeles where the fires occurred. However, the planning involved in these systems management is far more complex than it seems. As California works to diversify the water systems to better adapt to the impacts of climate change, it will be critical to understand the role the water-energy nexus plays in ensuring the resilience of our water systems, as well as a continued reduction in greenhouse gas (GHG) emissions.
California’s water system is a vast network of dams, reservoirs, power plants, pumping stations, and aqueducts, making it one of the most complex in the world3. Although 75 percent of the rain and snow in California comes from watersheds in the northern region of the state, the southern two-thirds of the state makes up 80 percent of the water demand4. As a result, California relies on three main water conveyance systems: the Central Valley Project (CVP), the State Water Project (SWP), and the Colorado Aqueduct. The CVP and SWP provide one-third of the state’s water supply and are managed by the California Department of Water Resources (DWR), while the Colorado Aqueduct, operated by the Metropolitan Water District of Southern California (MWD), provides Southern California with its primary source of water5. The SWP is California’s largest single electricity consumer due to the energy intensive process of transporting water over the Tehachapi Mountains, highlighting just one example of the water-energy nexus in the state.”6
California’s water systems are highly vulnerable to climate change. Recently, we have seen very wet years, causing flooding, followed by dry seasons with severe wildfires fueled by increased vegetation7. These fluctuations in weather patterns, fueled by climate change, have created prime scenarios for increasingly intense wildfires, heavy rain and flooding, and drought. Increases in average annual temperatures have contributed to weather whiplash, causing variable rain and runoff patterns that lead to extreme floods, droughts, and heightened wildfire risks. These conditions challenge water sector operators to plan and manage their systems effectively to address climate vulnerability.
Both DWR and MWD have developed comprehensive water management plans to address climate urgency and protect California’s water resources and watersheds as global temperatures continue to rise. Watersheds, critical points in the water systems, experience climate change uniquely based on local variables such as geography, hydrology, socioeconomic factors, land use patterns, and infrastructure. Therefore, all agencies involved in California’s water systems must have complementary regulatory frameworks and programs to provide coordinated and flexible guidance, assistance, and oversight. The consistent, widespread planning and management of California water systems is critical to preparing for the range of climate change impacts that could affect the state year-round. These interconnected systems are fragile and require a rigorous level of oversight and management. Reactive measures can disrupt the carefully planned systems that are managed from the state to the local level, therefore it is crucial for the sustainability of our water systems to proactively prepare for these extreme weather events.
As part of California’s strategy to prepare the state for a hotter, drier future, water agencies are working to conserve more water and diversify water supply, including through water recycling, groundwater recharge, stormwater capture, and desalination. While these processes will make the state more resilient to future climate change impacts, many of these activities can be energy-intensive and it is important to track the water-energy nexus of the state’s water systems in order to ensure that we are still on track to achieve emissions reduction goals while ensuring resilience of our water systems for current and future generations.
The Climate Registry’s Water-Energy Nexus (WEN) Registry empowers dozens of California’s water and wastewater agencies to measure, track, and mitigate their water-related emissions, in order to understand and limit their operations’ GHG emissions, and support our water systems to be resilient and sustainable as we adapt to our changing climate and the resulting extreme weather we are facing. The Water-Energy Nexus Registry Protocol provides guidance to quantify emissions from sources specific to the water and wastewater sectors, compile water-related data and performance metrics, identify opportunities for GHG emissions reductions, and track the impact of emissions reductions over time. Tools such as the WEN Registry provide water managers with the knowledge to ensure that they are still working to mitigate the impacts of climate change by reducing their GHG emissions, while implementing projects and infrastructure updates to adapt to more extreme weather events.
California’s ability to manage its water resources depends on proactive planning and emissions tracking. By leveraging tools like the WEN Registry, water agencies can reduce their carbon footprint while strengthening system resilience against climate change.
1 https://ww2.arb.ca.gov/wildfires-climate-change
2 https://water.ca.gov/Programs/All-Programs/Climate-Change-Program/Climate-Change-and-Water
3 https://water.ca.gov/water-basics/the-california-water-system
4 https://water.ca.gov/water-basics/the-california-water-system
5 https://water.ca.gov/water-basics/the-california-water-system
6 chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.ppic.org/wp-content/uploads/1020aer-appendix-c.pdf
7 https://sustainablela.ucla.edu/2025lawildfires