Scientists have built the case that heat waves and droughts are now more likely to mix in the United States than at any point in the nation’s history.

“Despite an apparent hiatus in rising temperature and no significant trend in droughts, we show a substantial increase in concurrent droughts and heatwaves across most parts of the United States,” Omid Mazdiyasni and Amir AghaKouchak, who study climate and hydrology trends at UC Irvine, wrote in a study published in the Proceedings of the National Academy of Sciences.

The study shows that in the 20 years between 1990 and 2010, heat waves and droughts took place simultaneously more frequently than between 1960 and 1980.  In most cases, the two overlapped more than 50% more during the latter period of time.

States along the southern portion of the nation faced the most occurrences of the combined factors.

The study also examined damage to society and overall health from the combination of the heat waves and drought.  They cited a situation in 2003 where Europe was struck with the combo and it lead directly or indirectly to 15,000 deaths in France.