California’s commitment to climate leadership is facing a new challenge as environmental advocates call for the state to address a “hidden” source of greenhouse gas emissions: water reservoirs. While the state aggressively tracks emissions from dairy farms, landfills, and the oil and gas industry, a coalition of organizations is urging regulators to begin monitoring the methane bubbling out of reservoirs.
The issue centers on the chemical process that occurs when rivers are dammed. As organic material accumulates in the reservoir and breaks down under low-oxygen conditions, it generates methane. This gas then escapes into the atmosphere, either by bubbling to the surface or being released through hydropower turbines. Given that methane is a potent greenhouse gas, its release from these managed water systems complicates the state’s image of hydropower as a purely “green” energy source.
A coalition including the clothing company Patagonia, Friends of the River, and Tell The Dam Truth has submitted a petition to the California Air Resources Board (CARB). The group is requesting that the state’s key emissions regulator require dam and reservoir operators to formally measure and report their greenhouse gas emissions to improve climate accounting.
The Science of Reservoir Emissions
Methane is recognized as the second-biggest contributor to climate change. According to data provided by Friends of the River, the warming effect of methane is 20 to 80 times stronger and faster than that of carbon dioxide which heats the atmosphere more intensely. This potency is why California has previously committed to a goal of cutting methane emissions by 40% by 2030.
The process of “degassing” occurs when water is released through turbines or when gas naturally rises from the reservoir floor. John Harrison, a professor at Washington State University’s School of the Environment, notes that reservoirs constitute an key source of methane. He suggests that tracking these emissions would allow California to make more informed decisions regarding the role of hydropower within its energy mix.
The scale of these emissions is significant. Estimates suggest that greenhouse gas emissions from California’s largest reservoirs are roughly equivalent to having 1.2 million gas-powered cars on the road every year according to analysis cited by environmental groups. Specific sites are highlighted as major contributors; for example, the San Luis Reservoir is estimated to emit more methane from turbine degassing than any other dam in the state.
Impact of New Infrastructure Projects
The debate over reservoir emissions has extended to planned infrastructure. The proposed Sites Reservoir has become a focal point for climate analysts. An analysis conducted by Patagonia and other environmental groups projected a large climate impact from the project, estimating that the Sites Reservoir alone would add emissions equivalent to approximately 80,000 additional cars on the road as part of its projected environmental footprint.
These findings challenge the traditional classification of hydropower as climate-friendly. By ignoring the methane produced by the decomposition of organic matter in reservoirs, critics argue that the state is maintaining a gap in its climate accounting that obscures the true cost of water storage and hydroelectric power.
Academic and Regulatory Efforts
While the petition to the California Air Resources Board seeks a regulatory mandate, academic research is already underway to quantify the problem. Researchers from UC Davis, including collaborators from the Department of Civil and Environmental Engineering and the Tahoe Environmental Research Center (TERC), have partnered with Valley Water. This partnership aims to study methane emissions specifically from reservoirs located in Northern California to better understand managed water systems.
The integration of this data into official state policy would represent a shift in how California manages its water-energy nexus. If the California Air Resources Board adopts the recommendations of the petitioning coalition, dam operators would be required to transition from estimated emissions to verified, reported data.
Key Takeaways on Reservoir Methane
- The Process: Organic matter breaks down in low-oxygen reservoir environments, creating methane that bubbles to the surface or exits via turbines.
- Climate Impact: Methane is 20-80 times more potent than carbon dioxide in terms of warming effect.
- The Scale: Large California reservoirs are estimated to produce emissions equivalent to 1.2 million gas-powered cars annually.
- Policy Goal: Environmental groups are petitioning the California Air Resources Board to mandate reporting of these emissions.
- Research: UC Davis and TERC are currently studying methane emissions in Northern California reservoirs.
The next critical step in this process is the response from the California Air Resources Board regarding the petition submitted by the coalition of environmental groups and Patagonia. The outcome will determine whether reservoir operators must begin formal greenhouse gas reporting to close the current gap in the state’s climate accounting.
We invite our readers to share their thoughts on the balance between water security and climate emissions in the comments below.