LOS ANGELES (AP) — California heat waves are trending toward being more humid with elevated nighttime temperatures and are becoming stronger in populous coastal areas, a new study by climate researchers found.

The trend contrasts with classic California heat waves that occur in interior desert and valley areas and typically have hot days and dryness and cooling at night, the American Geophysical Union said Wednesday in a statement.

The study was conducted by researchers at the Scripps Institution of Oceanography/University of California, San Diego, and will be published in the AGU publication Geophysical Research Letters.

Researchers Alexander Gershunov and Kristen Guirguis said the trend has human health implications for heavily populated coastal regions and could in turn trigger changes there such as in energy demand.

"Coastal communities are acclimated to cooler mean temperatures and are not well prepared for extreme heat either physiologically or technologically through air conditioning use," Guirguis said.

"Populations tend to adapt to changes in their average conditions but extreme events can catch people off-guard. An increase in heat wave intensity relative to average conditions could mean much more heat-related illness during heat waves unless effective heat emergency plans are implemented."

The study used an approach reflecting that what has been considered extreme heat is gradually becoming commonplace, the release said. That meant the researchers projected heat wave intensity against a backdrop of increasing summertime temperatures instead of defining heat waves relative to fixed temperature thresholds.

"The advantage of using this evolving 'non-stationary' definition is that heat waves remain extreme events even under much warmer climate," said Gershunov.

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