Thousands of power plants worldwide face sharp reductions in electricity output by mid-century due to more frequent heatwaves and drought driven by global warming, according to a study published Monday.

"We need to be concerned as electricity will become more expensive and less reliable in the future due to climate change," co-author Keywan Riahi of the International Institute for Applied Systems Analysis in Austria told AFP.

If warming continues unchecked, higher temperatures and water shortages could, by 2050, cut capacity in hydro-electric plants by nearly four percent, and in thermoelectric plants -- powered by fossil fuels, nuclear power or biomass -- by 12 percent.

Even if the target embraced at the Paris climate summit in December is met -- limiting global temperature rise to less than two degrees Celsius (3.6 degrees Fahrenheit) compared to pre-industrial levels -- power capacity would still drop significantly, according to the research.

Hydro- and thermoelectric plants, which together provide 98 percent of the global electricity supply, both depend on water to cool machinery or generate power.

Improvements in efficiency and switching types of fuel, however, would be one way to avoid future shortages of water and power, the study said.

Especially vulnerable regions include the United States, southern South America, southern Africa, central and southern Europe, and southeast Asia.

The study analysed data from nearly four-fifths of the world's hydro-electric plants, and more than a quarter of thermoelectric ones.

"Many of the plants that we couldn't include in our analysis will be vulnerable to climate change as well, but we simply didn't have the information," Riahi said by email.

Water consumption for power generation is expected to double within 40 years, according to the study, published in Nature Climate Change.

In many regions, this vastly expanded consumption will clash head on -- particularly in rapidly expanding economies -- with increased demands from agriculture and domestic use, neither of which are taken into account in this study.

"Climate change will amplify this competition, reduce reliability of the systems, and increase the risk of water and electric shortages," Riahi commented.

"However, there is the possibility to adapt" in both types of power plants, he added.