New Study Quantifies Impact of Droughts on Emissions Due to Power Generation from Fossil Fuels as Alternative

There was an increase in emissions of harmful air pollutants and carbon dioxide from power generation plants in various western U.S. states due to the recent droughts. The reason was the increased use of fossil fuels as an alternative to hampered hydroelectric power. The impact has been measured by a new study.

Maps show the median estimated cumulative emissions in 11 western states. (Image credit: Diffenbaugh Lab)

During a drought, as there is a deficiency in hydropower, the western U.S. states tend to increase power generation, as well as emissions, from fossil fuels. A new study at the Stanford University shows that from 2001 to 2015, nearly 10% of the average annual carbon dioxide emissions from power generation in California, Idaho, Oregon, and Washington was caused by droughts.

Water is used in electricity generation, both directly for hydropower and indirectly for cooling in thermoelectric power plants. We find that in a number of western states where hydropower plays a key role in the clean energy portfolio, droughts cause an increase in emissions as natural gas or coal-fired power plants are brought online to pick up the slack when water for hydropower comes up short.”

Noah Diffenbaugh, Professor, Stanford Earth.

Noah is a climate scientist, the Kara J. Foundation professor in Stanford’s School of Earth, Energy & Environmental Sciences (Stanford Earth), and senior author of the study

According to the study, which was reported in the December 21st, 2018, issue of Environmental Research Letters, emissions of sulfur dioxide and nitrogen oxides—air pollutants that could cause lung irritation and lead to acid rain and smog—also increased in certain states due to droughts. Some of the predominant increases in sulfur dioxide occurred in Colorado, Utah, Washington, and Wyoming. The most significant increases in nitrogen oxides took place in California, Colorado, Oregon, Utah, Washington, and Wyoming.

Challenges to going carbon-free

Overall, the scientists discovered that from 2001 to 2015, drought-induced changes in energy sources caused the release of an additional 100 million tons of carbon dioxide in 11 western U.S. states. That is equivalent to adding 1.4 million vehicles to the roadways in the region in a year. Nearly 51 million tons were contributed to the total by the power sector in California, which has a mandate to go carbon-free by 2045. Washington, where it is anticipated that the legislature in January 2019 will consider a proposal to avoid the use of fossil fuels for electricity generation by 2045, contributed almost 22 million tons.

For California, Oregon and Washington, which generate a lot of hydropower, the drought-induced increases in carbon dioxide emissions represent substantial fractions of their Clean Power Plan targets.

Julio Herrera-Estrada, Study Lead Author and Postdoctoral Researcher, Stanford Earth.

Legislated in 2015, the Clean Power Plan set up countrywide restrictions on greenhouse gas emissions from power plants. Although the policy has been retrenched under the Trump administration, Herrera-Estrada says it is still a valuable benchmark for targets that may be eventually by states or the federal government for the electricity sector.

In recent years, the western U.S. states have born the brunt of severe droughts that have been expected by researchers to become more common in various parts across the globe with the continuing global warming. According to the new study, failure to be ready for the emissions effect of these droughts could render achieving air quality and climate goals more challenging.

To have reliable and clean electricity, you have to make sure you have an energy portfolio that’s diverse, such that low-emissions electricity sources are able to kick in during a drought when hydropower cannot fully operate.

Julio Herrera-Estrada, Study Lead Author and Postdoctoral Researcher, Stanford Earth.

Assessing the West

The western United States is a perfect testing ground for perceiving the relationships between droughts and emissions from the power sector. Apart from the copious data from recent droughts, the scientists were able to explore how emissions vary with different types of backup power plants since states across the area have a range of energy mixes.

The scientists predicted that total emissions of sulfur dioxide, carbon dioxide, and nitrogen oxides from natural gas and coal-fueled power plants were related to the droughts from 2001 to 2015.

For instance, Colorado tends to increase coal-fired power plants when there is a decline in hydropower, whereas California and Idaho ramp up power generation from natural gas. Oregon, Washington, and Wyoming tend to ramp up both. In Wyoming and Montana, coal generation is partially increased so that the electricity can be exported to adjacent states that are also experiencing decreases in power generation as a result of drought.

For decades, people have been looking at the impacts of droughts on food security and agriculture. We’re less aware of exactly how droughts impact the energy sector and pollutant emissions in a quantitative and systematic way.

Julio Herrera-Estrada, Study Lead Author and Postdoctoral Researcher, Stanford Earth.

Earlier attempts to gain insights into the way drought influences electricity have largely depended on power plant models, which need scientists to make assumptions in relation to factors like the efficiencies of the plants and decisions on allocation of water resources. For this study, the researchers investigated the statistics provided by the U.S. Energy Information Administration and the U.S. Environmental Protection Agency.

Herrera-Estrada stated that the new study can assist in validating prevalent models, which can then be subsequently used to gain a comprehensive picture of the risks due to the droughts and to inform attempts to reduce drought-induced emissions.

Apart from the American West, similar emission increases could be driven by droughts in places that usually rely heavily on hydropower and switch to coal, natural gas, or petroleum when there is a shortfall in waterways.

Other parts of the world depend on hydropower even more than the western U.S.,” stated Diffenbaugh, who is also Kimmelman Family senior fellow at Stanford’s Woods Institute for the Environment. “Our results suggest that hydro-dependent regions may need to consider not only primary generation but also backup generation in order to meet emissions reduction targets, such as those in the UN Paris Agreement.”

The study was funded by the NASA Earth and Space Science Fellowship, NOAA, the Department of Energy, and Stanford University.

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