Hydroelectric drought: How climate change is complicating California’s plans for a carbon-free future

A view of Lake Oroville at 96% capacity on May 11, 2016 (right) and in drought conditions on July 26, 2021 (left). Move the cursor to reveal the photos. (Kelly M. Grow / California Department of Water Resources)

I grew up in the generally dry, inland southern California, so droughts aren’t entirely unexpected for me, my neighbors, or my coworkers. Since I was born in 1987, the state has experienced four long droughts: the 1987-1992 drought, the 2007-2009 drought which contributed to one of the state’s worst wildfire seasons, the drought from 2011 to 2017 which is the longest drought on record in California, and the current drought which started in 2020 and continues to worsen. I grew up hearing warnings about water shortages and high temperatures.

While experiencing a few years of drought is not entirely new to the inhabitants of the arid Southwest, what is new is the intensity and duration of the current droughts, due to climate change caused by our dependence. to fossil fuels to meet our energy needs. There is also some evidence that what is considered a typical California climate is unusually humid compared to long-term historical trends for the region. In the future, climate change is expected to lead to longer and more intense droughts in terms of rainfall scarcity. This will affect California’s water supply and other systems that depend on it, namely hydroelectric generating resources.

Lower water levels. California is already experiencing the effects of climate change-induced droughts on hydroelectric resources. As recently as last week, the Edward Hyatt Lake Oroville Power Plant had to cease hydroelectric production for the first time since it was built in 1967. Water levels in Lake Powell, a reservoir on the Colorado River upstream of the Lake Mead, which supplies the Hoover Dam and its export of electricity to California, also fell to their lowest level since the 1930s. During the California drought of 2011-2017, utilities made up for lost hydroelectric production by increasing their reliance on natural gas power plants to avoid blackouts, causing a 33% increase in annual carbon dioxide emissions from 2012 to 2014.

The impacts of drought on hydropower affect the power system in the short and long term. In the short term, a continued lack of water supply throughout this summer and potentially in the following years will again lead to increased dependence on natural gas. While the California production mix has started to incorporate more renewables and energy storage, these resources are not yet large enough to compensate for a significant reduction in hydropower production, which is typically 15-20%. of the state’s electricity supply in years without drought.

As we see with Lake Powell, hydropower production does not simply decrease in proportion to the decrease in water availability: if water reservoir levels fall below the height of intake levels for hydropower turbines , the installation must completely cease the production of electricity. When reduced water availability is combined with record high temperatures and wildfires, such as the Bootleg Fire in Oregon that has threatened power lines to California, the loss of hydropower can lead to losses. high electricity prices and potential blackouts.

The key role of hydropower. In the long term, California will need to factor the effects of climate change into state plans to develop a zero-carbon power system. Hydropower can potentially play an important role in achieving state goals in a cost-effective and materially efficient manner. This is because hydropower belongs to a class of resources that do not produce greenhouse gas emissions during their operation and can provide electricity to ensure that electrical loads are met when variable wind and solar production. is low and other energy storage systems are exhausted.

Research on how best to develop a zero carbon power system generally shows that having controllable resources – those that are available on demand, not just when the wind is blowing or the sun is shining – as part of the process. mix can enable grids to meet one given the goal of lower cost decarbonization (and lower material throughput) than trying to do so with wind, solar and energy storage alone. Debates are ongoing over the types of controllable zero-carbon resources that should or should not be included in a future power system, particularly in relation to nuclear and biomass. Hydropower, however, is often present in the design of future systems, due to its demonstrated ability to operate flexibly and its already large existing capacity in the United States and around the world. The U.S. Department of Energy’s HydroWIRES initiative, an ongoing research program to better understand the capabilities of hydropower resources to support future power grids, recognizes the value of hydropower across the United States. While the use of hydropower to support future power systems does not come without issues that need to be addressed, such as managing flows to protect endangered fish, hydropower has the potential to play a role. essential in zero carbon power systems.

Modification of water availability models. The ability of hydropower resources to provide the short-term benefits of avoiding the additional use of natural gas (and its associated emissions), as well as the long-term benefits of enabling the development of reliable zero-carbon electricity systems and affordable, depends on the availability of water both in total and during times when the electricity grid needs it most. Climate change is expected to alter patterns of water availability for hydropower by intensifying and lengthening storms during wet periods and droughts during dry periods. Even if the total amount of water supplied to reservoirs does not change, a change in the timing of rainfall affects the ability of hydropower plants to act as back-up systems for variable renewable energy resources.

For example, in California, precipitation has historically occurred during the fall and winter months as snow, creating a significant snowpack in the high elevation mountains of the state. In the spring, the snowpack melts, sending water to the reservoirs for storage. This ensures that water is available to meet the high summer demands for water and electricity. In a warming climate, however, precipitation in the fall and winter is expected to intensify and fall as rain instead of snow. Instead of replenishing the snowpack of the mountains, this rain will increase inflows from reservoirs. A sudden increase in runoff can cause reservoirs to fill to capacity, forcing operators to release any additional influx to avoid structural failure, meaning not all precipitation will be stored.

During the summer, droughts are expected to last longer than past events, and the water stored in California reservoirs may not be enough to meet summer’s highest electricity demands. If California plans its zero-carbon electricity system based on historic hydropower availability, but achieves lower availability due to climate change, the state may not meet its zero-carbon electricity targets or run the risk of power outages.

Taking into account climate change. Going forward, there are two categories of actions California can take to reduce the impacts of climate change on hydroelectric resources. The first is to take into account the effects of climate change on water availability in the operational practices of hydropower reservoirs, by developing updated water release schedules that forecast more variable future inflows rather than historical inflow patterns. The details of what these changes will look like will vary from reservoir to reservoir, as each reservoir is subject to different inflow patterns and operated under different constraints and priorities outside of hydropower generation.

The second set of actions consists of taking into account the effects of climate change on the availability of hydroelectric production as part of the resource mix that will feed the future zero carbon electricity grid. Including these impacts in modeling the expansion of state capacity, which inform planning decisions, will allow planners to better understand the extent to which other resources (such as geothermal or thermal storage). energy, for example) will need to be further developed to compensate for changes in the availability of hydropower resources in a warmer climate.


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