Proc. Natl Acad. Sci. USA http://doi.org/7hj (2015)

Climate extremes, such as heatwaves and droughts, have important impacts on food, water and energy supplies with detrimental effects on human health and well-being. The co-occurrence of two extreme events can intensify the individual impacts, causing even more damage.

Credit: RICHARD MASON / ISTOCK / THINKSTOCK

Omid Mazdiyasni and Amir AghaKouchak, from the University of California at Irvine, US, show that the concurrence of heatwaves and droughts, termed compound events, has significantly increased in the US. They evaluated daily temperature and monthly precipitation records between 1960 and 2010 to determine trends in these events.

The intensity and duration of these compound events has increased in the south, southeast and some parts of the western United States, despite no observed trend in drought-only occurrences. Furthermore, the frequency of longer, more severe compound events has increased more than for shorter, less severe ones. Understanding how climate change will affect the trends in concurrences of climate extremes is essential for effective planning and adaptation in susceptible areas.