Partners in crime: U.S. heat waves, droughts occuring together more frequently

The double whammy of overlapping droughts and heat waves is happening more frequently than it used to, according to a new study by climate scientists.

“Heat waves can kill people and crops while worsening air quality, and droughts exacerbate those serious impacts,” said lead author Amir AghaKouchak, an environmental engineer from the University of California, Irvine.

When these two extremes happen at the same time, the threats to the environment and society are far more significant, he added.

The study — published Monday in the Proceedings of the National Academy of Sciences — also found that the more intense the heat wave, the greater likelihood that it happened at the same time as a drought.

The study focused on the U.S., and compared 1960 to 1980 with 1990 to 2010. It found that heat waves and droughts happened together much more frequently in the latter time period.

The chance of these events occurring together was highest across the southern U.S., from New Mexico to Alabama, scientists said. The two climate events were least likely to occur at the same time in the northern states and portions of the Midwest.

While the researchers did not include man-made climate change in this study, AghaKouchak said, an overall increase in temperatures worldwide is raising the chances of heat waves.

2014 was the warmest year on record for the Earth, the National Centers for Environmental Information said, and 2015 is likely to break that record.