Droughts and high temperatures caused by climate change could play havoc with the electricity supply of the Western United States, say engineers in a study published in Nature Climate Change. As of 2010, more than 90 percent of America's electricity is generated by thermoelectric power stations — facilities that use heat to create electricity, from burning coal to nuclear power. Many plant like this, however, rely on water for cooling, with these facilities accounting for 45 percent of water withdrawals in 2010 (these figures are calculated every five years) — more than agriculture. If there's less water in the nation's rivers or even if that water is just hotter than normal then power stations won't be able operate at full capacity. And as the recent drought in California shows, this is more than just a speculative scenario.

46 percent of Western America's power stations are "vulnerable"

Based on simulations covering 14 states and 978 power stations in the Western US, engineers from Arizona State University suggest that in half a century, vulnerable facilities could lose anywhere between 1.1 to 3 percent of their summertime capacity. Power stations classed as "vulnerable" make up 46 percent of total capacity in the West and include not only thermoelectric plants, but also renewable sources such as hydroelectricity, wind turbines, and solar plants. The scientists note that in the case of a 10-year drought event, capacity could drop by as much as 8.8 percent.

These may sound like small figures, but power providers work within fairly slim margins of error, calculating how much electricity is left over after meeting peak expected demand. "In the West, this margin is typically between 10 to 20 percent, although in some areas it may be in the single digits." Matthew Bartos, one of the paper's two authors, tells The Verge. "In this context, a capacity reduction of a few percentage points could mean the difference between meeting demand and having to buy electricity from a neighboring power provider."

Droughts in California in 2001 led to $2.5 to $6 billion in economic losses

Severe drops in capacity beyond the grid's capacity could lead to outages but could also inflict economic damage. In 2001, for example, when severe droughts in California and the Pacific Northwest throttled hydroelectric power generation, electricity prices rose steeply and the region sustained somewhere between $2.5 and $6 billion in economic losses. The researchers add that the threat to the West's electricity supply is compounded by the fact that when the weather is extremely hot, people use more electricity — mostly to power air conditioning — but that the study's findings can't be applied to the rest of the US, as not only does the climate differ, but also the underlying power infrastructure.

Currently, power companies aren't doing enough to factor in the affect of climate change on electricity supply, say the paper's authors. While they do note that upgrades to existing plants and new technology may offset the "penalties imposed by climate change," this is far from certain. They add that while renewable energy sources are far from immune to the effects of climate change, they fare better than traditional methods such as steam and combustion turbines. "Renewables are more resilient to the effects of climate change," they write, and their increased use would contribute to "a more climate-resistant power infrastructure."