The effects of climate change could hamper electric generating capacity in the Western U.S. during peak summertime energy use by about 3 percent on average, and up to nearly 9 percent if there is ongoing drought.

A new study from Arizona State University looked at the effects of climate change on streamflow, air and water temperature, humidity and air density. The result is that by mid-century, nearly half of existing capacity operating in the Western Electricity Coordinating Council, which spans 14 states, could be adversely affected to some degree.

Some of the largest capacity reductions would be in Colorado, Utah and Wyoming, although California would likely see the most widespread effects. It is the desert Southwest that would be hit the hardest, however, according to lead author Matt Bartos, research scientist at ASU’s Fulton School of Engineering. The study appeared in the May issue of Nature Climate Change.

“In their development plans, power providers are not taking into account climate-change impacts,” Bartos said in a statement. “They are likely overestimating their ability to meet future electricity needs.” An electric utility survey by Black & Veatch found that reliability, regulation and cybersecurity ranked as top concerns; climate change does not make the list as a standalone concern. 

Combustion turbines will see the most consistent capacity reductions, the study found, although steam turbines will be the most affected by drought. Many renewables, including wind and solar PV, will fare much better, but they are not immune. The study found utility-scale solar PV could also see summertime capacity reductions of about 1 percent due to higher air temperatures.

Hydropower is one of the sources that will be directly affected, although the outcomes vary across the region. The Northwest is expected to receive more rain under climate-change forecasts, while California will continue to see less. Hydropower losses in California have already cost California ratepayers about $1.4 billion in the past three years.

With some planning, however, the expected losses due to changing climate conditions could be made up by wind, solar PV and demand-side management. Utility-scale solar generation, along with more natural gas, made up the deficit of hydropower in California in 2014.

Other forces, such as older coal-fired power plants being retired due to increasing regulation, could also take many of the most affected generation sources offline by mid-century. The U.S. Environmental Protection Agency’s Clean Power Plan would also increase the trend to retire the least efficient, and usually most water-hungry, power plants.

Finally, energy efficiency and demand response, often the cheapest ways to meet demand during peak summer days, could assume a far larger role in the future, especially in California, where the rules for demand response are being rewritten to allow for broader participation.